[PATCH] Reduce performance penalty for turned off traces

[PATCH] Reduce performance penalty for turned off traces

[gennady.kupava]

From: Gennady Kupava <gkupava@bloomberg.net>

Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
---
One of the tasks siggested in scope of 'Git sprint weekend'.
Couple of chioces made here:
 1. Use constant instead of NULL to indicate default trace level, this just
makes everything simpler.
 2. Move just enough from implementation to header, to be able to do check
before calling actual functions.
 3. Most controversail: do not support optimization for older compilers not
supporting variadic templates in macroses. Problem is that theoretically
someone may write some complicated trace while would work in 'modern' compiler and be too slow in more 'classic' compilers, however expectation is that risk of that is quite low and 'classic' compilers will go away eventually.

Passes test suite locally on Linux/amd64.

 trace.c | 29 ++++++----------------------
 trace.h | 68 +++++++++++++++++++++++++++++++++++++++++++++++------------------
 2 files changed, 55 insertions(+), 42 deletions(-)

diff --git a/trace.c b/trace.c
index 7508aea02..180ee3b00 100644
--- a/trace.c
+++ b/trace.c
@@ -25,26 +25,14 @@
 #include "cache.h"
 #include "quote.h"
 
-/*
- * "Normalize" a key argument by converting NULL to our trace_default,
- * and otherwise passing through the value. All caller-facing functions
- * should normalize their inputs in this way, though most get it
- * for free by calling get_trace_fd() (directly or indirectly).
- */
-static void normalize_trace_key(struct trace_key **key)
-{
-	static struct trace_key trace_default = { "GIT_TRACE" };
-	if (!*key)
-		*key = &trace_default;
-}
+struct trace_key trace_default_key = { TRACE_KEY_PREFIX, 0, 0, 0 };
+struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
 
 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
 {
 	const char *trace;
 
-	normalize_trace_key(&key);
-
 	/* don't open twice */
 	if (key->initialized)
 		return key->fd;
@@ -82,8 +70,6 @@ static int get_trace_fd(struct trace_key *key)
 
 void trace_disable(struct trace_key *key)
 {
-	normalize_trace_key(&key);
-
 	if (key->need_close)
 		close(key->fd);
 	key->fd = 0;
@@ -129,7 +115,6 @@ static int prepare_trace_line(const char *file, int line,
 static void trace_write(struct trace_key *key, const void *buf, unsigned len)
 {
 	if (write_in_full(get_trace_fd(key), buf, len) < 0) {
-		normalize_trace_key(&key);
 		warning("unable to write trace for %s: %s",
 			key->key, strerror(errno));
 		trace_disable(key);
@@ -168,13 +153,13 @@ static void trace_argv_vprintf_fl(const char *file, int line,
 {
 	struct strbuf buf = STRBUF_INIT;
 
-	if (!prepare_trace_line(file, line, NULL, &buf))
+	if (!prepare_trace_line(file, line, &trace_default_key, &buf))
 		return;
 
 	strbuf_vaddf(&buf, format, ap);
 
 	sq_quote_argv(&buf, argv, 0);
-	print_trace_line(NULL, &buf);
+	print_trace_line(&trace_default_key, &buf);
 }
 
 void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
@@ -189,8 +174,6 @@ void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 	print_trace_line(key, &buf);
 }
 
-static struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
-
 static void trace_performance_vprintf_fl(const char *file, int line,
 					 uint64_t nanos, const char *format,
 					 va_list ap)
@@ -216,7 +199,7 @@ void trace_printf(const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
-	trace_vprintf_fl(NULL, 0, NULL, format, ap);
+	trace_vprintf_fl(NULL, 0, &trace_default_key, format, ap);
 	va_end(ap);
 }
 
@@ -341,7 +324,7 @@ void trace_repo_setup(const char *prefix)
 
 int trace_want(struct trace_key *key)
 {
-	return !!get_trace_fd(key);
+       return !!get_trace_fd(key);
 }
 
 #if defined(HAVE_CLOCK_GETTIME) && defined(HAVE_CLOCK_MONOTONIC)
diff --git a/trace.h b/trace.h
index 179b249c5..64326573a 100644
--- a/trace.h
+++ b/trace.h
@@ -4,6 +4,8 @@
 #include "git-compat-util.h"
 #include "strbuf.h"
 
+#define TRACE_KEY_PREFIX "GIT_TRACE"
+
 struct trace_key {
 	const char * const key;
 	int fd;
@@ -11,7 +13,10 @@ struct trace_key {
 	unsigned int  need_close : 1;
 };
 
-#define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
+#define TRACE_KEY_INIT(name) { TRACE_KEY_PREFIX "_" #name, 0, 0, 0 }
+
+extern struct trace_key trace_default_key;
+extern struct trace_key trace_perf_key;
 
 extern void trace_repo_setup(const char *prefix);
 extern int trace_want(struct trace_key *key);
@@ -77,24 +82,49 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
  * comma, but this is non-standard.
  */
 
-#define trace_printf(...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, NULL, __VA_ARGS__)
-
-#define trace_printf_key(key, ...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__)
-
-#define trace_argv_printf(argv, ...) \
-	trace_argv_printf_fl(TRACE_CONTEXT, __LINE__, argv, __VA_ARGS__)
-
-#define trace_strbuf(key, data) \
-	trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data)
-
-#define trace_performance(nanos, ...) \
-	trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos, __VA_ARGS__)
-
-#define trace_performance_since(start, ...) \
-	trace_performance_fl(TRACE_CONTEXT, __LINE__, getnanotime() - (start), \
-			     __VA_ARGS__)
+#define trace_pass(key) ((key)->fd || !(key)->initialized)
+
+#define trace_printf(...)						    \
+	do {								    \
+		if (trace_pass(&trace_default_key))			    \
+			trace_printf_key_fl(TRACE_CONTEXT, __LINE__,        \
+					    &trace_default_key,__VA_ARGS__);\
+	} while(0)
+
+#define trace_printf_key(key, ...)					    \
+	do {								    \
+		if (trace_pass(key))					    \
+			trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
+					    __VA_ARGS__);		    \
+	} while(0)
+
+#define trace_argv_printf(argv, ...)					    \
+	do {								    \
+		if (trace_pass(&trace_default_key))			    \
+		       trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,	    \
+					    argv, __VA_ARGS__);		    \
+	} while(0)
+
+#define trace_strbuf(key, data)						    \
+	do {								    \
+		if (trace_pass(key))					    \
+			trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
+	} while(0)
+
+#define trace_performance(nanos, ...)					    \
+	do {								    \
+		if (trace_pass(key))					    \
+			trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
+					     __VA_ARGS__);  		    \
+	} while(0)
+
+#define trace_performance_since(start, ...)				    \
+	do {								    \
+		if (trace_pass(&trace_perf_key))			    \
+			trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
+					     getnanotime() - (start),	    \
+					     __VA_ARGS__);		    \
+	} while(0)
 
 /* backend functions, use non-*fl macros instead */
 __attribute__((format (printf, 4, 5)))
-- 
2.14.1

Re: [PATCH] Reduce performance penalty for turned off traces

[Jeff King]

On Sat, Nov 11, 2017 at 07:28:58PM +0000, gennady.kupava@gmail.com wrote:

> From: Gennady Kupava <gkupava@bloomberg.net>
> 
> Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>

Thanks, and welcome to the list.

> ---
> One of the tasks siggested in scope of 'Git sprint weekend'.
> Couple of chioces made here:

These kinds of choices/caveats (along with the motivation for the patch)
should go into the commit message so people running "git log" later can
see them.

>  1. Use constant instead of NULL to indicate default trace level, this just
> makes everything simpler.

I think this makes sense, as we were translating NULL into this default
struct behind the scenes already. As we discussed off-list, this does
mean that you can no longer do:

  trace_printf_key(NULL, "foo");

to send to the default key, and instead must do:

  trace_printf("foo");

The second one has always been the preferred way of spelling it, but the
first one happened to work. So the only fallout would be if somebody is
using the non-preferred method, they'd now segfault. There aren't any
such calls in the current code base, though, and I find it rather
unlikely that there would be new instances in topics other people are
working on.

I think it may be worth splitting that out into a separate preparatory
patch to make it more clear what's going on (especially if our
assumption turns out wrong and somebody does end up tracing a problem
back to it).

>  2. Move just enough from implementation to header, to be able to do check
> before calling actual functions.

Makes sense.

>  3. Most controversail: do not support optimization for older
>     compilers not supporting variadic templates in macroses. Problem
>     is that theoretically someone may write some complicated trace
>     while would work in 'modern' compiler and be too slow in more
>     'classic' compilers, however expectation is that risk of that is
>     quite low and 'classic' compilers will go away eventually.

I think this is probably acceptable. I know we've discussed elsewhere
recently how common such compilers actually are, and whether we could
give up on them altogether.

If we wanted to, we could support that case by using inline functions in
the header (though it does make me wonder if compilers that old also do
not actually end up inlining).

I did manually disable HAVE_VARIADIC_MACROS and confirmed that the
result builds and passes the test suite (though I suspect that GIT_TRACE
is not well exercised by the suite).

> diff --git a/trace.c b/trace.c
> index 7508aea02..180ee3b00 100644
> --- a/trace.c
> +++ b/trace.c
> @@ -25,26 +25,14 @@
>  #include "cache.h"
>  #include "quote.h"
>  
> -/*
> - * "Normalize" a key argument by converting NULL to our trace_default,
> - * and otherwise passing through the value. All caller-facing functions
> - * should normalize their inputs in this way, though most get it
> - * for free by calling get_trace_fd() (directly or indirectly).
> - */
> -static void normalize_trace_key(struct trace_key **key)
> -{
> -	static struct trace_key trace_default = { "GIT_TRACE" };
> -	if (!*key)
> -		*key = &trace_default;
> -}
> +struct trace_key trace_default_key = { TRACE_KEY_PREFIX, 0, 0, 0 };

Makes sense. We no longer auto-normalize, but just expect the
appropriate functions to pass a pointer to the default key themselves.

> +struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);

This change was unexpected, but I think you just moved this up to keep
all the pre-declared structs together. Makes sense.

>  /* Get a trace file descriptor from "key" env variable. */
>  static int get_trace_fd(struct trace_key *key)
>  {
>  	const char *trace;
>  
> -	normalize_trace_key(&key);
> -
>  	/* don't open twice */
>  	if (key->initialized)
>  		return key->fd;

And this and similar changes to drop normalize_trace_key() all make
sense with the earlier hunk. Good.

> @@ -341,7 +324,7 @@ void trace_repo_setup(const char *prefix)
>  
>  int trace_want(struct trace_key *key)
>  {
> -	return !!get_trace_fd(key);
> +       return !!get_trace_fd(key);
>  }

This line accidentally swapped out the tab for spaces.

> diff --git a/trace.h b/trace.h
> index 179b249c5..64326573a 100644
> --- a/trace.h
> +++ b/trace.h
> @@ -4,6 +4,8 @@
>  #include "git-compat-util.h"
>  #include "strbuf.h"
>  
> +#define TRACE_KEY_PREFIX "GIT_TRACE"
> [..]
> -#define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
> +#define TRACE_KEY_INIT(name) { TRACE_KEY_PREFIX "_" #name, 0, 0, 0 }

I see you pulled this out so you could use TRACE_KEY_PREFIX elsewhere
for the default key. Yes, the default key and the prefix do happen to be
related in that way, but I actually think it was a bit less obfuscated
the original way, even it repeated the string "GIT_TRACE" twice.

> +#define trace_pass(key) ((key)->fd || !(key)->initialized)

Factoring this out makes sense, since we have to repeat it in each
macro.

Speaking of macros, one side effect of this whole patch is that the
"key" parmaeter is going to be evaluated multiple times. I think that's
an acceptable tradeoff, as we'd basically always expect to pass the
address of a static struct here.

If that's a problem I think we _could_ do it with a combination of
macros and inline functions. The macro has to go in the outer layer in
order to set __LINE__ properly. But something like:

  static inline
  void trace_printf_key_helper(const char *context, int line,
                               struct trace_key *key,
			       const char *fmt, ...)
  {
	if (trace_pass(key)) {
		va_list ap;
		va_start(ap, fmt);
		trace_vprintf_key_fl(context, line, key, fmt, ap);
		va_end(ap);
	}
  }

  #define trace_printf_key(key, ...) \
	trace_printf_key_helper(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__);

would work, I think.

> +#define trace_printf(...)						    \
> +	do {								    \
> +		if (trace_pass(&trace_default_key))			    \
> +			trace_printf_key_fl(TRACE_CONTEXT, __LINE__,        \
> +					    &trace_default_key,__VA_ARGS__);\
> +	} while(0)
> +
> +#define trace_printf_key(key, ...)					    \
> +	do {								    \
> +		if (trace_pass(key))					    \
> +			trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
> +					    __VA_ARGS__);		    \
> +	} while(0)

Now that these definitions are getting a bit more complex, I wonder if
we can implement them in terms of each other. I.e., could the first one
be:

  #define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)

I'm not sure if there are any gotchas with recursive variadic macros. If
it's just this one macro that's not too big a deal, and it looks like
most of the rest of them end up having to call different functions and
can't nest like this. So it may not be worth troubling about.

> +#define trace_argv_printf(argv, ...)					    \
> [...]

The rest of this looks good.

I tried timing a simple loop like:

diff --git a/git.c b/git.c
index 9e96dd4090..f3dbc15a99 100644
--- a/git.c
+++ b/git.c
@@ -626,6 +626,11 @@ int cmd_main(int argc, const char **argv)
 {
 	const char *cmd;
 	int done_help = 0;
+	int i;
+
+	for (i = 0; i < 1000000; i++)
+		trace_printf("item %d", i);
+	return 0;
 
 	cmd = argv[0];
 	if (!cmd)

Without your patch, the times for GIT_TRACE=1 and GIT_TRACE=0 are about
500ms and 9ms respectively.

After your patch, the GIT_TRACE=1 time remains the same but GIT_TRACE=0
drops to 1ms.

So it is measurable, and we might expect that tracing a really big loop
(say over all of the objects in the repository) would benefit. OTOH, a
real loop would actually be doing other stuff, so the speedup would be
less dramatic. Still, it seems like an easy win.

-Peff

Re: [PATCH] Reduce performance penalty for turned off traces

[Gennady Kupava]

Hi Jeff, thanks for such detailed review and additional testing.

Below are just some discussion related review comments,
Please expect patch itself on some evening during coming week.

On 12 November 2017 at 14:17, Jeff King <peff@peff.net> wrote:
>
> On Sat, Nov 11, 2017 at 07:28:58PM +0000, gennady.kupava@gmail.com wrote:
>
> > From: Gennady Kupava <gkupava@bloomberg.net>
> >
> > Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
>
> Thanks, and welcome to the list.
>
>
> > ---
> > One of the tasks siggested in scope of 'Git sprint weekend'.
> > Couple of chioces made here:
>
> These kinds of choices/caveats (along with the motivation for the patch)
> should go into the commit message so people running "git log" later can
> see them.

Will split into two patches.

>
> >  1. Use constant instead of NULL to indicate default trace level, this just
> > makes everything simpler.
>
> I think this makes sense, as we were translating NULL into this default
> struct behind the scenes already. As we discussed off-list, this does
> mean that you can no longer do:
>
>   trace_printf_key(NULL, "foo");
>
> to send to the default key, and instead must do:
>
>   trace_printf("foo");
>
> The second one has always been the preferred way of spelling it, but the
> first one happened to work. So the only fallout would be if somebody is
> using the non-preferred method, they'd now segfault. There aren't any
> such calls in the current code base, though, and I find it rather
> unlikely that there would be new instances in topics other people are
> working on.
>
> I think it may be worth splitting that out into a separate preparatory
> patch to make it more clear what's going on (especially if our
> assumption turns out wrong and somebody does end up tracing a problem
> back to it).


Logic which lead me to removing NULL:
_If_ we want to do some kind of trivial check before calling functions
from other
translation units (which is always real function call), we have to
have some kind
of status immediately available in .h file.
I saw two options here:
 - move whole 'normalization' procedure to .h
 - remove 'normalization' procedure

Reasons removal option was chosen:
 - I found no code which actually uses NULL as a parameter option.
 - Given the nature of the key parameter ( struct key* )
I was just really unable to find any reasonable use
case there caller really want to pass NULL, so it seemed to me that
best solution
is to remove it. I still can imagine something like dynamic trace
category coming from
some kind of configuration file. In such special case there caller
might need it,
he might just do check in calling code once or just simply add it.
 - Squash big more performance as we do not need to do this
normalization on every call.

I will elaborate on 'moving whole implementation later'

>
> >  2. Move just enough from implementation to header, to be able to do check
> > before calling actual functions.
>
> Makes sense.
>
> >  3. Most controversail: do not support optimization for older
> >     compilers not supporting variadic templates in macroses. Problem
> >     is that theoretically someone may write some complicated trace
> >     while would work in 'modern' compiler and be too slow in more
> >     'classic' compilers, however expectation is that risk of that is
> >     quite low and 'classic' compilers will go away eventually.
>
> I think this is probably acceptable. I know we've discussed elsewhere
> recently how common such compilers actually are, and whether we could
> give up on them altogether.
>
> If we wanted to, we could support that case by using inline functions in
> the header (though it does make me wonder if compilers that old also do
> not actually end up inlining).
>
> I did manually disable HAVE_VARIADIC_MACROS and confirmed that the
> result builds and passes the test suite (though I suspect that GIT_TRACE
> is not well exercised by the suite).
>

Good.

>
> > diff --git a/trace.c b/trace.c
> > index 7508aea02..180ee3b00 100644
> > --- a/trace.c
> > +++ b/trace.c
> > @@ -25,26 +25,14 @@
> >  #include "cache.h"
> >  #include "quote.h"
> >
> > -/*
> > - * "Normalize" a key argument by converting NULL to our trace_default,
> > - * and otherwise passing through the value. All caller-facing functions
> > - * should normalize their inputs in this way, though most get it
> > - * for free by calling get_trace_fd() (directly or indirectly).
> > - */
> > -static void normalize_trace_key(struct trace_key **key)
> > -{
> > -     static struct trace_key trace_default = { "GIT_TRACE" };
> > -     if (!*key)
> > -             *key = &trace_default;
> > -}
> > +struct trace_key trace_default_key = { TRACE_KEY_PREFIX, 0, 0, 0 };
>
> Makes sense. We no longer auto-normalize, but just expect the
> appropriate functions to pass a pointer to the default key themselves.

This is again (more details below) choice of how much implementation details we
want to move into header file.

>
>
> > +struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
>
> This change was unexpected, but I think you just moved this up to keep
> all the pre-declared structs together. Makes sense.
>

Reason is that _if_ we want to cover trace_performance* macroses with
our performance patch, we need to expose this implementation detail in
header file now.
And I expect we do want, even if this interface is not used now.

> >  /* Get a trace file descriptor from "key" env variable. */
> >  static int get_trace_fd(struct trace_key *key)
> >  {
> >       const char *trace;
> >
> > -     normalize_trace_key(&key);
> > -
> >       /* don't open twice */
> >       if (key->initialized)
> >               return key->fd;
>
> And this and similar changes to drop normalize_trace_key() all make
> sense with the earlier hunk. Good.
>
> > @@ -341,7 +324,7 @@ void trace_repo_setup(const char *prefix)
> >
> >  int trace_want(struct trace_key *key)
> >  {
> > -     return !!get_trace_fd(key);
> > +       return !!get_trace_fd(key);
> >  }
>
> This line accidentally swapped out the tab for spaces.

Will fix that.

>
> > diff --git a/trace.h b/trace.h
> > index 179b249c5..64326573a 100644
> > --- a/trace.h
> > +++ b/trace.h
> > @@ -4,6 +4,8 @@
> >  #include "git-compat-util.h"
> >  #include "strbuf.h"
> >
> > +#define TRACE_KEY_PREFIX "GIT_TRACE"
> > [..]
> > -#define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
> > +#define TRACE_KEY_INIT(name) { TRACE_KEY_PREFIX "_" #name, 0, 0, 0 }
>
> I see you pulled this out so you could use TRACE_KEY_PREFIX elsewhere
> for the default key. Yes, the default key and the prefix do happen to be
> related in that way, but I actually think it was a bit less obfuscated
> the original way, even it repeated the string "GIT_TRACE" twice.

Yeah, I thought for some time here as I don't like both approaches,
slight duplication vs
slight complication. Typically I choose slight complication, but now,
giving this another
thought it seems like slight duplication is really better in this case.

>
> > +#define trace_pass(key) ((key)->fd || !(key)->initialized)
>
> Factoring this out makes sense, since we have to repeat it in each
> macro.
>
> Speaking of macros, one side effect of this whole patch is that the
> "key" parmaeter is going to be evaluated multiple times. I think that's
> an acceptable tradeoff, as we'd basically always expect to pass the
> address of a static struct here.

Yes, I though about this.

>
> If that's a problem I think we _could_ do it with a combination of
> macros and inline functions.

Agree. Actually there is solution to this specific problem
which somehow didn't came to my mind yesterday. There is actually no
reason for trace_pass to be a macro, it is better to make it an inline function.

> The macro has to go in the outer layer in
> order to set __LINE__ properly. But something like:
>
>   static inline
>   void trace_printf_key_helper(const char *context, int line,
>                                struct trace_key *key,
>                                const char *fmt, ...)
>   {
>         if (trace_pass(key)) {
>                 va_list ap;
>                 va_start(ap, fmt);
>                 trace_vprintf_key_fl(context, line, key, fmt, ap);
>                 va_end(ap);
>         }
>   }
>
>   #define trace_printf_key(key, ...) \
>         trace_printf_key_helper(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__);
>
> would work, I think.

It would but...

So I think main question in this whole idea to optimize traces a bit is how much
we really want and need to move to header. All reasons here are quite marginal,
but whole task is quite marginal, so we have to operate in terms of
marginal reasons.

So, i took into what gcc actually generated in optimized assembly for this code
(of course not in details, but just to find how much calls made). My expectation
was that gcc as one of best compilers optimize all that static
functions into one, so we'll have
something like one big function call to the functions which somewhere
on top will do
the check which is similar to trace_pass.

In reality, gcc didn't do that and I saw 3 function calls. I am pretty
sure that compiler
of the distant bright future will do that, and only problem would be
to eliminate that
single function call. Hopefully with -flto it will also eliminate this
single functions call,
at it will be able to see through translation units. Given that I
actually like current
implementation as it hides all details in .c file.

Noting on the side at this point that first theoretical conclusion
here is that even if we'll move whole
trace.c into trace.h we'll still have same 2-3 function calls.

So, now given the description above, what's the best way to improve performance,
if we want?
We need to somehow do check in header, so gcc could inline that into
calling function.
Now, how much of implementation details we want to move to header?
I think it is good if we hide inside .c whatever we can.
So my solution was to keep all logic in implementation, move only
necessary things to header,
so:
 - reader of header file would see as few implementation details as possible
 - compiler would not try to inline something which actually doesn't matter
   (it only matters to inline something which checks if traces are
off). As this trace.h is included
   (indirectly) pretty much everywhere (287 object files out of 315),
not trying to re-compile and inline
   things that many times will save some CPU cycles during build
reducing build time and probably
   even saving some non-binary trees =)

Now, implementation you suggesting moves extra things into .h,
so it is imperfect in terms above, while things I suggested moves only
necessary bit
of checking the necessity to do anything, which is only (interesting) part
should be executed while traces are off, and the only part we really
want to be inlined.

That's the reasons, hopefully it makes sense, if not, I just don't see
much difference
and could implement it in different way.

>
> > +#define trace_printf(...)                                                \
> > +     do {                                                                \
> > +             if (trace_pass(&trace_default_key))                         \
> > +                     trace_printf_key_fl(TRACE_CONTEXT, __LINE__,        \
> > +                                         &trace_default_key,__VA_ARGS__);\
> > +     } while(0)
> > +
> > +#define trace_printf_key(key, ...)                                       \
> > +     do {                                                                \
> > +             if (trace_pass(key))                                        \
> > +                     trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
> > +                                         __VA_ARGS__);                   \
> > +     } while(0)
>
> Now that these definitions are getting a bit more complex, I wonder if
> we can implement them in terms of each other. I.e., could the first one
> be:
>
>   #define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
>
> I'm not sure if there are any gotchas with recursive variadic macros. If
> it's just this one macro that's not too big a deal, and it looks like
> most of the rest of them end up having to call different functions and
> can't nest like this. So it may not be worth troubling about.

I was not sure about variadic macro calling variadic macro as well, so
decided to not do that.
Now I read that two lines in C99 standard related to __VA_ARGS__, it
seems like nothing
preventing that, so will do.

>
> > +#define trace_argv_printf(argv, ...)                                     \
> > [...]
>
> The rest of this looks good.
>
> I tried timing a simple loop like:
>
> diff --git a/git.c b/git.c
> index 9e96dd4090..f3dbc15a99 100644
> --- a/git.c
> +++ b/git.c
> @@ -626,6 +626,11 @@ int cmd_main(int argc, const char **argv)
>  {
>         const char *cmd;
>         int done_help = 0;
> +       int i;
> +
> +       for (i = 0; i < 1000000; i++)
> +               trace_printf("item %d", i);
> +       return 0;
>
>         cmd = argv[0];
>         if (!cmd)
>
> Without your patch, the times for GIT_TRACE=1 and GIT_TRACE=0 are about
> 500ms and 9ms respectively.

Well, still something measurable =) May be on some exotic hardware it
could be more...

> After your patch, the GIT_TRACE=1 time remains the same but GIT_TRACE=0
> drops to 1ms.
>
> So it is measurable, and we might expect that tracing a really big loop
> (say over all of the objects in the repository) would benefit. OTOH, a
> real loop would actually be doing other stuff, so the speedup would be
> less dramatic. Still, it seems like an easy win.

I actually quite familiar with performance analysis and know how to
use perf and similar tools a bit -
so if there is something more measurable in TODO, I could try. But I
guess this is
interesting to many devs so such tasks probably already all done and bottlenecks
are identified in git =)

With best regards,
Gennady

On 12 November 2017 at 14:17, Jeff King <peff@peff.net> wrote:
> On Sat, Nov 11, 2017 at 07:28:58PM +0000, gennady.kupava@gmail.com wrote:
>
>> From: Gennady Kupava <gkupava@bloomberg.net>
>>
>> Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
>
> Thanks, and welcome to the list.
>
>> ---
>> One of the tasks siggested in scope of 'Git sprint weekend'.
>> Couple of chioces made here:
>
> These kinds of choices/caveats (along with the motivation for the patch)
> should go into the commit message so people running "git log" later can
> see them.
>
>>  1. Use constant instead of NULL to indicate default trace level, this just
>> makes everything simpler.
>
> I think this makes sense, as we were translating NULL into this default
> struct behind the scenes already. As we discussed off-list, this does
> mean that you can no longer do:
>
>   trace_printf_key(NULL, "foo");
>
> to send to the default key, and instead must do:
>
>   trace_printf("foo");
>
> The second one has always been the preferred way of spelling it, but the
> first one happened to work. So the only fallout would be if somebody is
> using the non-preferred method, they'd now segfault. There aren't any
> such calls in the current code base, though, and I find it rather
> unlikely that there would be new instances in topics other people are
> working on.
>
> I think it may be worth splitting that out into a separate preparatory
> patch to make it more clear what's going on (especially if our
> assumption turns out wrong and somebody does end up tracing a problem
> back to it).
>
>>  2. Move just enough from implementation to header, to be able to do check
>> before calling actual functions.
>
> Makes sense.
>
>>  3. Most controversail: do not support optimization for older
>>     compilers not supporting variadic templates in macroses. Problem
>>     is that theoretically someone may write some complicated trace
>>     while would work in 'modern' compiler and be too slow in more
>>     'classic' compilers, however expectation is that risk of that is
>>     quite low and 'classic' compilers will go away eventually.
>
> I think this is probably acceptable. I know we've discussed elsewhere
> recently how common such compilers actually are, and whether we could
> give up on them altogether.
>
> If we wanted to, we could support that case by using inline functions in
> the header (though it does make me wonder if compilers that old also do
> not actually end up inlining).
>
> I did manually disable HAVE_VARIADIC_MACROS and confirmed that the
> result builds and passes the test suite (though I suspect that GIT_TRACE
> is not well exercised by the suite).
>
>> diff --git a/trace.c b/trace.c
>> index 7508aea02..180ee3b00 100644
>> --- a/trace.c
>> +++ b/trace.c
>> @@ -25,26 +25,14 @@
>>  #include "cache.h"
>>  #include "quote.h"
>>
>> -/*
>> - * "Normalize" a key argument by converting NULL to our trace_default,
>> - * and otherwise passing through the value. All caller-facing functions
>> - * should normalize their inputs in this way, though most get it
>> - * for free by calling get_trace_fd() (directly or indirectly).
>> - */
>> -static void normalize_trace_key(struct trace_key **key)
>> -{
>> -     static struct trace_key trace_default = { "GIT_TRACE" };
>> -     if (!*key)
>> -             *key = &trace_default;
>> -}
>> +struct trace_key trace_default_key = { TRACE_KEY_PREFIX, 0, 0, 0 };
>
> Makes sense. We no longer auto-normalize, but just expect the
> appropriate functions to pass a pointer to the default key themselves.
>
>> +struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
>
> This change was unexpected, but I think you just moved this up to keep
> all the pre-declared structs together. Makes sense.
>
>>  /* Get a trace file descriptor from "key" env variable. */
>>  static int get_trace_fd(struct trace_key *key)
>>  {
>>       const char *trace;
>>
>> -     normalize_trace_key(&key);
>> -
>>       /* don't open twice */
>>       if (key->initialized)
>>               return key->fd;
>
> And this and similar changes to drop normalize_trace_key() all make
> sense with the earlier hunk. Good.
>
>> @@ -341,7 +324,7 @@ void trace_repo_setup(const char *prefix)
>>
>>  int trace_want(struct trace_key *key)
>>  {
>> -     return !!get_trace_fd(key);
>> +       return !!get_trace_fd(key);
>>  }
>
> This line accidentally swapped out the tab for spaces.
>
>> diff --git a/trace.h b/trace.h
>> index 179b249c5..64326573a 100644
>> --- a/trace.h
>> +++ b/trace.h
>> @@ -4,6 +4,8 @@
>>  #include "git-compat-util.h"
>>  #include "strbuf.h"
>>
>> +#define TRACE_KEY_PREFIX "GIT_TRACE"
>> [..]
>> -#define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
>> +#define TRACE_KEY_INIT(name) { TRACE_KEY_PREFIX "_" #name, 0, 0, 0 }
>
> I see you pulled this out so you could use TRACE_KEY_PREFIX elsewhere
> for the default key. Yes, the default key and the prefix do happen to be
> related in that way, but I actually think it was a bit less obfuscated
> the original way, even it repeated the string "GIT_TRACE" twice.
>
>> +#define trace_pass(key) ((key)->fd || !(key)->initialized)
>
> Factoring this out makes sense, since we have to repeat it in each
> macro.
>
> Speaking of macros, one side effect of this whole patch is that the
> "key" parmaeter is going to be evaluated multiple times. I think that's
> an acceptable tradeoff, as we'd basically always expect to pass the
> address of a static struct here.
>
> If that's a problem I think we _could_ do it with a combination of
> macros and inline functions. The macro has to go in the outer layer in
> order to set __LINE__ properly. But something like:
>
>   static inline
>   void trace_printf_key_helper(const char *context, int line,
>                                struct trace_key *key,
>                                const char *fmt, ...)
>   {
>         if (trace_pass(key)) {
>                 va_list ap;
>                 va_start(ap, fmt);
>                 trace_vprintf_key_fl(context, line, key, fmt, ap);
>                 va_end(ap);
>         }
>   }
>
>   #define trace_printf_key(key, ...) \
>         trace_printf_key_helper(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__);
>
> would work, I think.
>
>> +#define trace_printf(...)                                                \
>> +     do {                                                                \
>> +             if (trace_pass(&trace_default_key))                         \
>> +                     trace_printf_key_fl(TRACE_CONTEXT, __LINE__,        \
>> +                                         &trace_default_key,__VA_ARGS__);\
>> +     } while(0)
>> +
>> +#define trace_printf_key(key, ...)                                       \
>> +     do {                                                                \
>> +             if (trace_pass(key))                                        \
>> +                     trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
>> +                                         __VA_ARGS__);                   \
>> +     } while(0)
>
> Now that these definitions are getting a bit more complex, I wonder if
> we can implement them in terms of each other. I.e., could the first one
> be:
>
>   #define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
>
> I'm not sure if there are any gotchas with recursive variadic macros. If
> it's just this one macro that's not too big a deal, and it looks like
> most of the rest of them end up having to call different functions and
> can't nest like this. So it may not be worth troubling about.
>
>> +#define trace_argv_printf(argv, ...)                                     \
>> [...]
>
> The rest of this looks good.
>
> I tried timing a simple loop like:
>
> diff --git a/git.c b/git.c
> index 9e96dd4090..f3dbc15a99 100644
> --- a/git.c
> +++ b/git.c
> @@ -626,6 +626,11 @@ int cmd_main(int argc, const char **argv)
>  {
>         const char *cmd;
>         int done_help = 0;
> +       int i;
> +
> +       for (i = 0; i < 1000000; i++)
> +               trace_printf("item %d", i);
> +       return 0;
>
>         cmd = argv[0];
>         if (!cmd)
>
> Without your patch, the times for GIT_TRACE=1 and GIT_TRACE=0 are about
> 500ms and 9ms respectively.
>
> After your patch, the GIT_TRACE=1 time remains the same but GIT_TRACE=0
> drops to 1ms.
>
> So it is measurable, and we might expect that tracing a really big loop
> (say over all of the objects in the repository) would benefit. OTOH, a
> real loop would actually be doing other stuff, so the speedup would be
> less dramatic. Still, it seems like an easy win.
>
> -Peff

Re: [PATCH] Reduce performance penalty for turned off traces

[Stefan Beller]

On Sun, Nov 12, 2017 at 6:17 AM, Jeff King <peff@peff.net> wrote:
> On Sat, Nov 11, 2017 at 07:28:58PM +0000, gennady.kupava@gmail.com wrote:
>
>> From: Gennady Kupava <gkupava@bloomberg.net>
>>
>> Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
>
> Thanks, and welcome to the list.

Welcome to the list!

> I did manually disable HAVE_VARIADIC_MACROS and confirmed that the
> result builds and passes the test suite (though I suspect that GIT_TRACE
> is not well exercised by the suite).

GIT_TRACE is exercised in the test suite (though I am not sure if it counts
as well-exercised) in t7406-submodule-update.sh for example, which uses
GIT_TRACE to obtain information about thread parallelism used by Git, as
that is not observable otherwise, if we assume that performance tests in the
standard test suite are not feasible.

> I tried timing a simple loop like:
> ....
> Without your patch, the times for GIT_TRACE=1 and GIT_TRACE=0 are about
> 500ms and 9ms respectively.
>
> After your patch, the GIT_TRACE=1 time remains the same but GIT_TRACE=0
> drops to 1ms.

So does that mean we can use a lot more tracing now?

Thanks,
Stefan

Re: [PATCH] Reduce performance penalty for turned off traces

[Jeff King]

On Sun, Nov 12, 2017 at 11:24:11PM +0000, Gennady Kupava wrote:

> In reality, gcc didn't do that and I saw 3 function calls. I am pretty
> sure that compiler of the distant bright future will do that, and only
> problem would be to eliminate that single function call. Hopefully
> with -flto it will also eliminate this single functions call, at it
> will be able to see through translation units. Given that I actually
> like current implementation as it hides all details in .c file.

Yeah, I agree with your analysis that we are really just overriding what
could eventually be figured out by the compiler during LTO.

I do think this is worth pursuing in the meantime, though, because it's
not _too_ much work, and we don't know when that magical optimizing
compiler will appear. :) So this frees us up in the meantime to worry
less about the cost of tracing.

> Now, implementation you suggesting moves extra things into .h, so it
> is imperfect in terms above, while things I suggested moves only
> necessary bit of checking the necessity to do anything, which is only
> (interesting) part should be executed while traces are off, and the
> only part we really want to be inlined.

I only meant to suggest moving the necessary checking into the .h file.
It's just that we have to make it a static inline for cases where we
don't have variadic macros. Anyway, I'm OK with your original notion of
leaving the non-variadic-macro systems on the "slow" path, so we can
just go with the pure-macro thing you have.

> > So it is measurable, and we might expect that tracing a really big loop
> > (say over all of the objects in the repository) would benefit. OTOH, a
> > real loop would actually be doing other stuff, so the speedup would be
> > less dramatic. Still, it seems like an easy win.
> 
> I actually quite familiar with performance analysis and know how to
> use perf and similar tools a bit -
> so if there is something more measurable in TODO, I could try. But I
> guess this is interesting to many devs so such tasks probably already
> all done and bottlenecks are identified in git =)

There are lots of bottlenecks still to be found, I'm sure. If you want
to have a go at finding some with perf, be my guest. :)

-Peff

Re: [PATCH] Reduce performance penalty for turned off traces

[Jeff King]

On Wed, Nov 15, 2017 at 11:14:20AM -0800, Stefan Beller wrote:

> > I did manually disable HAVE_VARIADIC_MACROS and confirmed that the
> > result builds and passes the test suite (though I suspect that GIT_TRACE
> > is not well exercised by the suite).
> 
> GIT_TRACE is exercised in the test suite (though I am not sure if it counts
> as well-exercised) in t7406-submodule-update.sh for example, which uses
> GIT_TRACE to obtain information about thread parallelism used by Git, as
> that is not observable otherwise, if we assume that performance tests in the
> standard test suite are not feasible.

Hmm, yeah, that might cover it. What I'm worried about is that we missed
some case where NULL needed to become &trace_default_key. But I did look
for that in my review of the patch and didn't notice any spots. And the
coverage in t7406 should help.

> > After your patch, the GIT_TRACE=1 time remains the same but GIT_TRACE=0
> > drops to 1ms.
> 
> So does that mean we can use a lot more tracing now?

Yep, that's the intent.

-Peff

[PATCH 1/2] Simplify tracing code by removing trace key normalization concept

[gennady.kupava]

From: Gennady Kupava <gkupava@bloomberg.net>

- to implement efficient traces with normalization, normalization
  implementation should be moved to header. as it seems better to not
  overload header file with this normalization logic, suggestion is
  just to remove it
- different macro exist specifically to handle traces with default key
- there is no use of normalization in current code
- it could be reintroduced if necessary

Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
---
 trace.c | 24 ++++--------------------
 trace.h |  4 +++-
 2 files changed, 7 insertions(+), 21 deletions(-)

diff --git a/trace.c b/trace.c
index cb1293ed3..d47ea28e8 100644
--- a/trace.c
+++ b/trace.c
@@ -24,26 +24,13 @@
 #include "cache.h"
 #include "quote.h"
 
-/*
- * "Normalize" a key argument by converting NULL to our trace_default,
- * and otherwise passing through the value. All caller-facing functions
- * should normalize their inputs in this way, though most get it
- * for free by calling get_trace_fd() (directly or indirectly).
- */
-static void normalize_trace_key(struct trace_key **key)
-{
-	static struct trace_key trace_default = { "GIT_TRACE" };
-	if (!*key)
-		*key = &trace_default;
-}
+struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
 
 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
 {
 	const char *trace;
 
-	normalize_trace_key(&key);
-
 	/* don't open twice */
 	if (key->initialized)
 		return key->fd;
@@ -81,8 +68,6 @@ static int get_trace_fd(struct trace_key *key)
 
 void trace_disable(struct trace_key *key)
 {
-	normalize_trace_key(&key);
-
 	if (key->need_close)
 		close(key->fd);
 	key->fd = 0;
@@ -128,7 +113,6 @@ static int prepare_trace_line(const char *file, int line,
 static void trace_write(struct trace_key *key, const void *buf, unsigned len)
 {
 	if (write_in_full(get_trace_fd(key), buf, len) < 0) {
-		normalize_trace_key(&key);
 		warning("unable to write trace for %s: %s",
 			key->key, strerror(errno));
 		trace_disable(key);
@@ -167,13 +151,13 @@ static void trace_argv_vprintf_fl(const char *file, int line,
 {
 	struct strbuf buf = STRBUF_INIT;
 
-	if (!prepare_trace_line(file, line, NULL, &buf))
+	if (!prepare_trace_line(file, line, &trace_default_key, &buf))
 		return;
 
 	strbuf_vaddf(&buf, format, ap);
 
 	sq_quote_argv(&buf, argv, 0);
-	print_trace_line(NULL, &buf);
+	print_trace_line(&trace_default_key, &buf);
 }
 
 void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
@@ -215,7 +199,7 @@ void trace_printf(const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
-	trace_vprintf_fl(NULL, 0, NULL, format, ap);
+	trace_vprintf_fl(NULL, 0, &trace_default_key, format, ap);
 	va_end(ap);
 }
 
diff --git a/trace.h b/trace.h
index 179b249c5..24b32f8f4 100644
--- a/trace.h
+++ b/trace.h
@@ -11,6 +11,8 @@ struct trace_key {
 	unsigned int  need_close : 1;
 };
 
+extern struct trace_key trace_default_key;
+
 #define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
 
 extern void trace_repo_setup(const char *prefix);
@@ -78,7 +80,7 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
  */
 
 #define trace_printf(...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, NULL, __VA_ARGS__)
+	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, &trace_default_key, __VA_ARGS__)
 
 #define trace_printf_key(key, ...) \
 	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__)
-- 
2.14.1

[PATCH 2/2] Reduce performance cost of the trace if trace category is disabled

[gennady.kupava]

From: Gennady Kupava <gkupava@bloomberg.net>

- Do the check if the trace key is enabled sooner in call chain.
- Move just enough code from trace.c into trace.h header so all code
  necessary to determine that trace is disabled could be inlined to
  calling functions.

Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
---
 trace.c |  3 +--
 trace.h | 58 ++++++++++++++++++++++++++++++++++++++++------------------
 2 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/trace.c b/trace.c
index d47ea28e8..b7530b51a 100644
--- a/trace.c
+++ b/trace.c
@@ -25,6 +25,7 @@
 #include "quote.h"
 
 struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
+struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
 
 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
@@ -172,8 +173,6 @@ void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 	print_trace_line(key, &buf);
 }
 
-static struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
-
 static void trace_performance_vprintf_fl(const char *file, int line,
 					 uint64_t nanos, const char *format,
 					 va_list ap)
diff --git a/trace.h b/trace.h
index 24b32f8f4..cd9e280ba 100644
--- a/trace.h
+++ b/trace.h
@@ -14,6 +14,7 @@ struct trace_key {
 extern struct trace_key trace_default_key;
 
 #define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
+extern struct trace_key trace_perf_key;
 
 extern void trace_repo_setup(const char *prefix);
 extern int trace_want(struct trace_key *key);
@@ -79,24 +80,42 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
  * comma, but this is non-standard.
  */
 
-#define trace_printf(...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, &trace_default_key, __VA_ARGS__)
-
-#define trace_printf_key(key, ...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__)
-
-#define trace_argv_printf(argv, ...) \
-	trace_argv_printf_fl(TRACE_CONTEXT, __LINE__, argv, __VA_ARGS__)
-
-#define trace_strbuf(key, data) \
-	trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data)
-
-#define trace_performance(nanos, ...) \
-	trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos, __VA_ARGS__)
-
-#define trace_performance_since(start, ...) \
-	trace_performance_fl(TRACE_CONTEXT, __LINE__, getnanotime() - (start), \
-			     __VA_ARGS__)
+#define trace_printf_key(key, ...)					    \
+	do {								    \
+		if (trace_pass_fl(key))					    \
+			trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
+					    __VA_ARGS__);		    \
+	} while(0)
+
+#define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__);
+
+#define trace_argv_printf(argv, ...)					    \
+	do {								    \
+		if (trace_pass_fl(&trace_default_key))			    \
+		       trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,	    \
+					    argv, __VA_ARGS__);		    \
+	} while(0)
+
+#define trace_strbuf(key, data)						    \
+	do {								    \
+		if (trace_pass_fl(key))					    \
+			trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
+	} while(0)
+
+#define trace_performance(nanos, ...)					    \
+	do {								    \
+		if (trace_pass_fl(key))					    \
+			trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
+					     __VA_ARGS__);  		    \
+	} while(0)
+
+#define trace_performance_since(start, ...)				    \
+	do {								    \
+		if (trace_pass_fl(&trace_perf_key))			    \
+			trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
+					     getnanotime() - (start),	    \
+					     __VA_ARGS__);		    \
+	} while(0)
 
 /* backend functions, use non-*fl macros instead */
 __attribute__((format (printf, 4, 5)))
@@ -110,6 +129,9 @@ extern void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 __attribute__((format (printf, 4, 5)))
 extern void trace_performance_fl(const char *file, int line,
 				 uint64_t nanos, const char *fmt, ...);
+inline int trace_pass_fl(struct trace_key *key) {
+	return key->fd || !key->initialized;
+}
 
 #endif /* HAVE_VARIADIC_MACROS */
 
-- 
2.14.1

Re: [PATCH 1/2] Simplify tracing code by removing trace key normalization concept

[Junio C Hamano]

gennady.kupava@gmail.com writes:

> Subject: Re: [PATCH 1/2] Simplify tracing code by removing trace key normalization concept

The usual style comment on the subject applies here.

> From: Gennady Kupava <gkupava@bloomberg.net>
>
> - to implement efficient traces with normalization, normalization
>   implementation should be moved to header. as it seems better to not
>   overload header file with this normalization logic, suggestion is
>   just to remove it
> - different macro exist specifically to handle traces with default key
> - there is no use of normalization in current code
> - it could be reintroduced if necessary

I cannot quite tell what it is trying to achive to make it a
bulleted list.  It's not like four things at the same conceptual
level is enumerated; instead it just has four sentences that talk
about random things.

More importantly, I am not sure I understand what these sentences
are trying to say.  "Should be moved to header"---so?  Does that
move something from the source to the header?  It seems to me that
the patch removes a helper function from trace.c but does not add
anything to the header.

Or am I wasting everybody's time by commenting on a stale comment
that used to describe an ancient iteration of this code?

Puzzled.

Re: [PATCH 2/2] Reduce performance cost of the trace if trace category is disabled

[Johannes Sixt]

Am 19.11.2017 um 01:42 schrieb gennady.kupava@gmail.com:
> +#define trace_printf_key(key, ...)					    \
> +	do {								    \
> +		if (trace_pass_fl(key))					    \
> +			trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
> +					    __VA_ARGS__);		    \
> +	} while(0)
> +
> +#define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__);
> +
> +#define trace_argv_printf(argv, ...)					    \
> +	do {								    \
> +		if (trace_pass_fl(&trace_default_key))			    \
> +		       trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,	    \
> +					    argv, __VA_ARGS__);		    \
> +	} while(0)
> +
> +#define trace_strbuf(key, data)						    \
> +	do {								    \
> +		if (trace_pass_fl(key))					    \
> +			trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
> +	} while(0)
> +
> +#define trace_performance(nanos, ...)					    \
> +	do {								    \
> +		if (trace_pass_fl(key))					    \

The token "key" here looks suspicious. Did you mean &trace_perf_key?

> +			trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
> +					     __VA_ARGS__);  		    \
> +	} while(0)
> +
> +#define trace_performance_since(start, ...)				    \
> +	do {								    \
> +		if (trace_pass_fl(&trace_perf_key))			    \
> +			trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
> +					     getnanotime() - (start),	    \
> +					     __VA_ARGS__);		    \
> +	} while(0)
>   
>   /* backend functions, use non-*fl macros instead */
>   __attribute__((format (printf, 4, 5)))

-- Hannes

Re: [PATCH 1/2] Simplify tracing code by removing trace key normalization concept

[Gennady Kupava]

> The usual style comment on the subject applies here.

Oh sure, 50 characters. 'Remove trace key normalization concept' would
be better?

> I cannot quite tell what it is trying to achive to make it a
bulleted list.  It's not like four things at the same conceptual
level is enumerated; instead it just has four sentences that talk
about random things.

With these four sentences I am describing the reasons why we need this
patch. In my previous iteration I had similar  description outside of
git comment and was told to move it into git description. So it is in
comments. Hot sure if I understand what is the problem here. I can
remove bulleted list and make it four sentences. I can remove it
altogether. I can add some text so it will be easier to understand
this without context of previous patch. What would be the best?

I reread relevant parts of
https://github.com/git/git/blob/master/Documentation/SubmittingPatches
and it seems description of the reasons and alternative discarded
solutions fits into description. So could please help me a bit to
understand what is wrong.

> More importantly, I am not sure I understand what these sentences
are trying to say.  "Should be moved to header"---so?  Does that
move something from the source to the header?  It seems to me that
the patch removes a helper function from trace.c but does not add
anything to the header.

I was told to split the patch and do removal for the normalization as
separate commit. As it is separate commit, it needs to do separate
description with the own reasons why etc. Yes it doesn't but it is
needed for the second patch in the series.

So comments explaining that, while implementing trace optimization, I
saw two options:
1. Move normalization function from .c file to .h file
2. Remove it

And why I choose removal - not used, would complicate header without
any benefit, and actually I didn't mention minor benefit of
compilation speed. This trace.h included and used in lots of places so
it will take compiler some time to actually eliminate the code.

> Puzzled.

Does it make more sense now?

Gennady


On 19 November 2017 at 02:19, Junio C Hamano <gitster@pobox.com> wrote:
> gennady.kupava@gmail.com writes:
>
>> Subject: Re: [PATCH 1/2] Simplify tracing code by removing trace key normalization concept
>
> The usual style comment on the subject applies here.
>
>> From: Gennady Kupava <gkupava@bloomberg.net>
>>
>> - to implement efficient traces with normalization, normalization
>>   implementation should be moved to header. as it seems better to not
>>   overload header file with this normalization logic, suggestion is
>>   just to remove it
>> - different macro exist specifically to handle traces with default key
>> - there is no use of normalization in current code
>> - it could be reintroduced if necessary
>
> I cannot quite tell what it is trying to achive to make it a
> bulleted list.  It's not like four things at the same conceptual
> level is enumerated; instead it just has four sentences that talk
> about random things.
>
> More importantly, I am not sure I understand what these sentences
> are trying to say.  "Should be moved to header"---so?  Does that
> move something from the source to the header?  It seems to me that
> the patch removes a helper function from trace.c but does not add
> anything to the header.
>
> Or am I wasting everybody's time by commenting on a stale comment
> that used to describe an ancient iteration of this code?
>
> Puzzled.

Re: [PATCH 2/2] Reduce performance cost of the trace if trace category is disabled

[Gennady Kupava]

Right, this trace is actually not used anywhere, so only check was
compilation. Will fix that.

On 19 November 2017 at 08:27, Johannes Sixt <j6t@kdbg.org> wrote:
> Am 19.11.2017 um 01:42 schrieb gennady.kupava@gmail.com:
>>
>> +#define trace_printf_key(key, ...)
>> \
>> +       do {
>> \
>> +               if (trace_pass_fl(key))
>> \
>> +                       trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,
>> \
>> +                                           __VA_ARGS__);
>> \
>> +       } while(0)
>> +
>> +#define trace_printf(...) trace_printf_key(&trace_default_key,
>> __VA_ARGS__);
>> +
>> +#define trace_argv_printf(argv, ...)
>> \
>> +       do {
>> \
>> +               if (trace_pass_fl(&trace_default_key))
>> \
>> +                      trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,
>> \
>> +                                           argv, __VA_ARGS__);
>> \
>> +       } while(0)
>> +
>> +#define trace_strbuf(key, data)
>> \
>> +       do {
>> \
>> +               if (trace_pass_fl(key))
>> \
>> +                       trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key,
>> data);\
>> +       } while(0)
>> +
>> +#define trace_performance(nanos, ...)
>> \
>> +       do {
>> \
>> +               if (trace_pass_fl(key))
>> \
>
>
> The token "key" here looks suspicious. Did you mean &trace_perf_key?
>
>> +                       trace_performance_fl(TRACE_CONTEXT, __LINE__,
>> nanos,\
>> +                                            __VA_ARGS__);
>> \
>> +       } while(0)
>> +
>> +#define trace_performance_since(start, ...)
>> \
>> +       do {
>> \
>> +               if (trace_pass_fl(&trace_perf_key))
>> \
>> +                       trace_performance_fl(TRACE_CONTEXT, __LINE__,
>> \
>> +                                            getnanotime() - (start),
>> \
>> +                                            __VA_ARGS__);
>> \
>> +       } while(0)
>>     /* backend functions, use non-*fl macros instead */
>>   __attribute__((format (printf, 4, 5)))
>
>
> -- Hannes

Re: [PATCH 1/2] Simplify tracing code by removing trace key normalization concept

[Junio C Hamano]

Gennady Kupava <gennady.kupava@gmail.com> writes:

>> The usual style comment on the subject applies here.
>
> Oh sure, 50 characters. 'Remove trace key normalization concept' would
> be better?

I was referring to #summary-section of Documentation/SubmittingPatches

    The first line of the commit message should be a short description (50
    characters is the soft limit, see DISCUSSION in linkgit:git-commit[1]),
    and should skip the full stop.  It is also conventional in most cases to
    prefix the first line with "area: " where the area is a filename or
    identifier for the general area of the code being modified, e.g.

    * doc: clarify distinction between sign-off and pgp-signing
    * githooks.txt: improve the intro section

    If in doubt which identifier to use, run `git log --no-merges` on the
    files you are modifying to see the current conventions.

    [[summary-section]]
    It's customary to start the remainder of the first line after "area: "
    with a lower-case letter. E.g. "doc: clarify...", not "doc:
    Clarify...", or "githooks.txt: improve...", not "githooks.txt:
    Improve...".

> So comments explaining that, while implementing trace optimization, I
> saw two options:
> 1. Move normalization function from .c file to .h file
> 2. Remove it
>
> And why I choose removal - not used, would complicate header without
> any benefit, and actually I didn't mention minor benefit of
> compilation speed. This trace.h included and used in lots of places so
> it will take compiler some time to actually eliminate the code.
>
>> Puzzled.
>
> Does it make more sense now?

The thought behind the change flows much better in the above
explanation than your four-bullet list (which a reader would often
assume are parallel and orthogonal).  "Remove this, because it is
not used" is the primary thing for this step, and the fact that the
later step benefit from that change, while it may be more important
to the person who want to see that later change, is incidental to
see if this change makes sense as a standalone patch.

And that primary thing, "remove this, because it is not used and
only complicates the code" is what we want to start the log message
with.  The first sentence ("this needs to be moved there") saying
what the patch chose not to was the source of the confusion.

Re: [PATCH 1/2] Simplify tracing code by removing trace key normalization concept

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> The thought behind the change flows much better in the above
> explanation than your four-bullet list (which a reader would often
> assume are parallel and orthogonal).  "Remove this, because it is
> not used" is the primary thing for this step, and the fact that the

Make that "because it is not strictly necessary", as that seems to
be much closer to what is going on, and I agree that it is a good
change to remove such "convenience for callers" feature from
codepaths that could be performance critical.  The callers can pass
the "&default" thing themselves just as easily as they pass NULL
and have the library code to do the defaulting, and that will remove
the need to incur extra cost for a subroutine call.

[PATCH 1/2] trace: remove trace key normalization

[gennady.kupava]

From: Gennady Kupava <gkupava@bloomberg.net>

Trace key normalization is not used, not strictly necessary,
complicates the code and would negatively affect compilation speed if
moved to header.

New trace_default_key key or existing separate marco could be used
instead of passing NULL as a key.

Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
---
 trace.c | 24 ++++--------------------
 trace.h |  4 +++-
 2 files changed, 7 insertions(+), 21 deletions(-)

diff --git a/trace.c b/trace.c
index cb1293ed3..d47ea28e8 100644
--- a/trace.c
+++ b/trace.c
@@ -24,26 +24,13 @@
 #include "cache.h"
 #include "quote.h"
 
-/*
- * "Normalize" a key argument by converting NULL to our trace_default,
- * and otherwise passing through the value. All caller-facing functions
- * should normalize their inputs in this way, though most get it
- * for free by calling get_trace_fd() (directly or indirectly).
- */
-static void normalize_trace_key(struct trace_key **key)
-{
-	static struct trace_key trace_default = { "GIT_TRACE" };
-	if (!*key)
-		*key = &trace_default;
-}
+struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
 
 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
 {
 	const char *trace;
 
-	normalize_trace_key(&key);
-
 	/* don't open twice */
 	if (key->initialized)
 		return key->fd;
@@ -81,8 +68,6 @@ static int get_trace_fd(struct trace_key *key)
 
 void trace_disable(struct trace_key *key)
 {
-	normalize_trace_key(&key);
-
 	if (key->need_close)
 		close(key->fd);
 	key->fd = 0;
@@ -128,7 +113,6 @@ static int prepare_trace_line(const char *file, int line,
 static void trace_write(struct trace_key *key, const void *buf, unsigned len)
 {
 	if (write_in_full(get_trace_fd(key), buf, len) < 0) {
-		normalize_trace_key(&key);
 		warning("unable to write trace for %s: %s",
 			key->key, strerror(errno));
 		trace_disable(key);
@@ -167,13 +151,13 @@ static void trace_argv_vprintf_fl(const char *file, int line,
 {
 	struct strbuf buf = STRBUF_INIT;
 
-	if (!prepare_trace_line(file, line, NULL, &buf))
+	if (!prepare_trace_line(file, line, &trace_default_key, &buf))
 		return;
 
 	strbuf_vaddf(&buf, format, ap);
 
 	sq_quote_argv(&buf, argv, 0);
-	print_trace_line(NULL, &buf);
+	print_trace_line(&trace_default_key, &buf);
 }
 
 void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
@@ -215,7 +199,7 @@ void trace_printf(const char *format, ...)
 {
 	va_list ap;
 	va_start(ap, format);
-	trace_vprintf_fl(NULL, 0, NULL, format, ap);
+	trace_vprintf_fl(NULL, 0, &trace_default_key, format, ap);
 	va_end(ap);
 }
 
diff --git a/trace.h b/trace.h
index 179b249c5..24b32f8f4 100644
--- a/trace.h
+++ b/trace.h
@@ -11,6 +11,8 @@ struct trace_key {
 	unsigned int  need_close : 1;
 };
 
+extern struct trace_key trace_default_key;
+
 #define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
 
 extern void trace_repo_setup(const char *prefix);
@@ -78,7 +80,7 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
  */
 
 #define trace_printf(...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, NULL, __VA_ARGS__)
+	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, &trace_default_key, __VA_ARGS__)
 
 #define trace_printf_key(key, ...) \
 	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__)
-- 
2.14.1

[PATCH 2/2] trace: improve performance while category is disabled

[gennady.kupava]

From: Gennady Kupava <gkupava@bloomberg.net>

- Do the check if the trace key is enabled sooner in call chain.
- Move just enough code from trace.c into trace.h header so all code
  necessary to determine that trace is disabled could be inlined to
  calling functions.

Signed-off-by: Gennady Kupava <gkupava@bloomberg.net>
---
 trace.c |  3 +--
 trace.h | 58 ++++++++++++++++++++++++++++++++++++++++------------------
 2 files changed, 41 insertions(+), 20 deletions(-)

diff --git a/trace.c b/trace.c
index d47ea28e8..b7530b51a 100644
--- a/trace.c
+++ b/trace.c
@@ -25,6 +25,7 @@
 #include "quote.h"
 
 struct trace_key trace_default_key = { "GIT_TRACE", 0, 0, 0 };
+struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
 
 /* Get a trace file descriptor from "key" env variable. */
 static int get_trace_fd(struct trace_key *key)
@@ -172,8 +173,6 @@ void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 	print_trace_line(key, &buf);
 }
 
-static struct trace_key trace_perf_key = TRACE_KEY_INIT(PERFORMANCE);
-
 static void trace_performance_vprintf_fl(const char *file, int line,
 					 uint64_t nanos, const char *format,
 					 va_list ap)
diff --git a/trace.h b/trace.h
index 24b32f8f4..db10f2afe 100644
--- a/trace.h
+++ b/trace.h
@@ -14,6 +14,7 @@ struct trace_key {
 extern struct trace_key trace_default_key;
 
 #define TRACE_KEY_INIT(name) { "GIT_TRACE_" #name, 0, 0, 0 }
+extern struct trace_key trace_perf_key;
 
 extern void trace_repo_setup(const char *prefix);
 extern int trace_want(struct trace_key *key);
@@ -79,24 +80,42 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
  * comma, but this is non-standard.
  */
 
-#define trace_printf(...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, &trace_default_key, __VA_ARGS__)
-
-#define trace_printf_key(key, ...) \
-	trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key, __VA_ARGS__)
-
-#define trace_argv_printf(argv, ...) \
-	trace_argv_printf_fl(TRACE_CONTEXT, __LINE__, argv, __VA_ARGS__)
-
-#define trace_strbuf(key, data) \
-	trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data)
-
-#define trace_performance(nanos, ...) \
-	trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos, __VA_ARGS__)
-
-#define trace_performance_since(start, ...) \
-	trace_performance_fl(TRACE_CONTEXT, __LINE__, getnanotime() - (start), \
-			     __VA_ARGS__)
+#define trace_printf_key(key, ...)					    \
+	do {								    \
+		if (trace_pass_fl(key))					    \
+			trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
+					    __VA_ARGS__);		    \
+	} while(0)
+
+#define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
+
+#define trace_argv_printf(argv, ...)					    \
+	do {								    \
+		if (trace_pass_fl(&trace_default_key))			    \
+		       trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,	    \
+					    argv, __VA_ARGS__);		    \
+	} while(0)
+
+#define trace_strbuf(key, data)						    \
+	do {								    \
+		if (trace_pass_fl(key))					    \
+			trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
+	} while(0)
+
+#define trace_performance(nanos, ...)					    \
+	do {								    \
+		if (trace_pass_fl(&trace_perf_key))			    \
+			trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
+					     __VA_ARGS__);  		    \
+	} while(0)
+
+#define trace_performance_since(start, ...)				    \
+	do {								    \
+		if (trace_pass_fl(&trace_perf_key))			    \
+			trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
+					     getnanotime() - (start),	    \
+					     __VA_ARGS__);		    \
+	} while(0)
 
 /* backend functions, use non-*fl macros instead */
 __attribute__((format (printf, 4, 5)))
@@ -110,6 +129,9 @@ extern void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 __attribute__((format (printf, 4, 5)))
 extern void trace_performance_fl(const char *file, int line,
 				 uint64_t nanos, const char *fmt, ...);
+inline int trace_pass_fl(struct trace_key *key) {
+	return key->fd || !key->initialized;
+}
 
 #endif /* HAVE_VARIADIC_MACROS */
 
-- 
2.14.1

Re: [PATCH 2/2] trace: improve performance while category is disabled

[Junio C Hamano]

gennady.kupava@gmail.com writes:

> From: Gennady Kupava <gkupava@bloomberg.net>
>
> - Do the check if the trace key is enabled sooner in call chain.
> - Move just enough code from trace.c into trace.h header so all code
>   necessary to determine that trace is disabled could be inlined to
>   calling functions.

Makes sense.  Will queue.

Thanks.

> +inline int trace_pass_fl(struct trace_key *key) {
> +	return key->fd || !key->initialized;
> +}

;-)

Re: [PATCH 2/2] trace: improve performance while category is disabled

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> gennady.kupava@gmail.com writes:
>
>> From: Gennady Kupava <gkupava@bloomberg.net>
>>
>> - Do the check if the trace key is enabled sooner in call chain.
>> - Move just enough code from trace.c into trace.h header so all code
>>   necessary to determine that trace is disabled could be inlined to
>>   calling functions.
>
> Makes sense.  Will queue.
>
> Thanks.

Just in case others notice style and whitespace issues, I've applied
the following to fix them, so there is no need to reroll only to fix
these.

diff --git a/trace.h b/trace.h
index db10f2afeb..05395242aa 100644
--- a/trace.h
+++ b/trace.h
@@ -85,29 +85,29 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
 		if (trace_pass_fl(key))					    \
 			trace_printf_key_fl(TRACE_CONTEXT, __LINE__, key,   \
 					    __VA_ARGS__);		    \
-	} while(0)
+	} while (0)
 
 #define trace_printf(...) trace_printf_key(&trace_default_key, __VA_ARGS__)
 
 #define trace_argv_printf(argv, ...)					    \
 	do {								    \
 		if (trace_pass_fl(&trace_default_key))			    \
-		       trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,	    \
+			trace_argv_printf_fl(TRACE_CONTEXT, __LINE__,	    \
 					    argv, __VA_ARGS__);		    \
-	} while(0)
+	} while (0)
 
 #define trace_strbuf(key, data)						    \
 	do {								    \
 		if (trace_pass_fl(key))					    \
 			trace_strbuf_fl(TRACE_CONTEXT, __LINE__, key, data);\
-	} while(0)
+	} while (0)
 
 #define trace_performance(nanos, ...)					    \
 	do {								    \
 		if (trace_pass_fl(&trace_perf_key))			    \
 			trace_performance_fl(TRACE_CONTEXT, __LINE__, nanos,\
-					     __VA_ARGS__);  		    \
-	} while(0)
+					     __VA_ARGS__);		    \
+	} while (0)
 
 #define trace_performance_since(start, ...)				    \
 	do {								    \
@@ -115,7 +115,7 @@ extern void trace_performance_since(uint64_t start, const char *format, ...);
 			trace_performance_fl(TRACE_CONTEXT, __LINE__,       \
 					     getnanotime() - (start),	    \
 					     __VA_ARGS__);		    \
-	} while(0)
+	} while (0)
 
 /* backend functions, use non-*fl macros instead */
 __attribute__((format (printf, 4, 5)))
@@ -129,7 +129,8 @@ extern void trace_strbuf_fl(const char *file, int line, struct trace_key *key,
 __attribute__((format (printf, 4, 5)))
 extern void trace_performance_fl(const char *file, int line,
 				 uint64_t nanos, const char *fmt, ...);
-inline int trace_pass_fl(struct trace_key *key) {
+inline int trace_pass_fl(struct trace_key *key)
+{
 	return key->fd || !key->initialized;
 }
 

Re: [PATCH 2/2] trace: improve performance while category is disabled

[Junio C Hamano]

Junio C Hamano <gitster@pobox.com> writes:

> Just in case others notice style and whitespace issues, I've applied
> the following to fix them, so there is no need to reroll only to fix
> these.
> ...
> -inline int trace_pass_fl(struct trace_key *key) {
> +inline int trace_pass_fl(struct trace_key *key)
> +{
>  	return key->fd || !key->initialized;
>  }

Spotted yet another.  This function in a header file, that is
included by many source files, must be made "static inline" (which I
already did as without the fix I couldn't get 'pu' to compile).

Re: [PATCH 2/2] trace: improve performance while category is disabled

[Gennady Kupava]

> Spotted yet another.  This function in a header file, that is
included by many source files, must be made "static inline" (which I
already did as without the fix I couldn't get 'pu' to compile).

Thanks, missed that, seems my compiler inlined all calls and I didn't
notice the problem.


On 27 November 2017 at 03:25, Junio C Hamano <gitster@pobox.com> wrote:
> Junio C Hamano <gitster@pobox.com> writes:
>
>> Just in case others notice style and whitespace issues, I've applied
>> the following to fix them, so there is no need to reroll only to fix
>> these.
>> ...
>> -inline int trace_pass_fl(struct trace_key *key) {
>> +inline int trace_pass_fl(struct trace_key *key)
>> +{
>>       return key->fd || !key->initialized;
>>  }
>
> Spotted yet another.  This function in a header file, that is
> included by many source files, must be made "static inline" (which I
> already did as without the fix I couldn't get 'pu' to compile).
>
>
>