Re: [PATCH v3] cat-file: skip expanding default format

[John Cai <johncai86@gmail.com>]

On 8 Mar 2022, at 18:09, John Cai wrote:

> Hi Taylor,
>
> On 8 Mar 2022, at 17:30, Taylor Blau wrote:
>
>> On Tue, Mar 08, 2022 at 10:08:46PM +0000, John Cai via GitGitGadget wrote:
>>> diff --git a/builtin/cat-file.c b/builtin/cat-file.c
>>> index 7b3f42950ec..e2edba70b41 100644
>>> --- a/builtin/cat-file.c
>>> +++ b/builtin/cat-file.c
>>> @@ -351,6 +351,13 @@ static void print_object_or_die(struct batch_options *opt, struct expand_data *d
>>>  	}
>>>  }
>>>
>>> +static int print_default_format(char *buf, int len, struct expand_data *data)
>>> +{
>>> +	return xsnprintf(buf, len, "%s %s %"PRIuMAX"\n", oid_to_hex(&data->oid),
>>> +			 type_name(data->type),
>>> +			 (uintmax_t)*data->info.sizep);
>>> +}
>>
>> Two small nits here. It looks like the indentation on the second and
>> third lines is off a little bit, since we'd typically expect those to be
>> indented to the same margin as the first argument to xsnprintf().
>
> Thanks for bringing this up. I did have a question about indentation in this
> case. for the second line, I did try to indent it to align with buf. I attempted
> to do the same with the third line, but it's the ( that lines up with buf so
> optically it looks a little off.
>
>>
>> The other is that you're reading data->info.sizep by dereferencing it,
>> but we know that it points to data->size. So I think there it makes
>> sense to just read the value directly out of data->size, though note
>> that you'll still need the cast to uintmax_t since you're formatting it
>> with PRIuMAX.
>
> good point, I'll adjust this in the next version.
>
>>
>>> +
>>>  /*
>>>   * If "pack" is non-NULL, then "offset" is the byte offset within the pack from
>>>   * which the object may be accessed (though note that we may also rely on
>>> @@ -381,10 +388,16 @@ static void batch_object_write(const char *obj_name,
>>>  		}
>>>  	}
>>>
>>> -	strbuf_reset(scratch);
>>> -	strbuf_expand(scratch, opt->format, expand_format, data);
>>> -	strbuf_addch(scratch, '\n');
>>> -	batch_write(opt, scratch->buf, scratch->len);
>>> +	if (!opt->format) {
>>> +		char buf[1024];
>>> +		int len = print_default_format(buf, 1024, data);
>>> +		batch_write(opt, buf, len);
>>
>> Just curious (and apologies if this was discussed earlier and I missed
>> it), but: is there a reason that we have to use a scratch buffer here
>> that is separate from the strbuf we already have allocated?
>>
>> That would avoid a large-ish stack variable, but it means that the two
>> paths are a little more similar, and can share the batch_write call
>> outside of the if/else statement.
>
> This was holdover code from before. Looks like the scratch buffer gets passed
> in. Do you mean we don't need to allocate char buf[1024] and instead we can just
> use scratch and pass it into print_default_format?

something like this?

diff --git a/builtin/cat-file.c b/builtin/cat-file.c
index e2edba70b418..2336bcc80850 100644
--- a/builtin/cat-file.c
+++ b/builtin/cat-file.c
@@ -351,11 +351,11 @@ static void print_object_or_die(struct batch_options *opt, struct expand_data *d
        }
 }

-static int print_default_format(char *buf, int len, struct expand_data *data)
+static void print_default_format(struct strbuf *scratch, struct expand_data *data)
 {
-       return xsnprintf(buf, len, "%s %s %"PRIuMAX"\n", oid_to_hex(&data->oid),
-                        type_name(data->type),
-                        (uintmax_t)*data->info.sizep);
+       strbuf_addf(scratch, "%s %s %"PRIuMAX"\n", oid_to_hex(&data->oid),
+                   type_name(data->type),
+                   (uintmax_t)data->size);
 }

 /*
@@ -388,17 +388,17 @@ static void batch_object_write(const char *obj_name,
                }
        }

+       strbuf_reset(scratch);
+
        if (!opt->format) {
-               char buf[1024];
-               int len = print_default_format(buf, 1024, data);
-               batch_write(opt, buf, len);
+               print_default_format(scratch, data);
        } else {
-               strbuf_reset(scratch);
                strbuf_expand(scratch, opt->format, expand_format, data);
                strbuf_addch(scratch, '\n');
-               batch_write(opt, scratch->buf, scratch->len);
        }

+       batch_write(opt, scratch->buf, scratch->len);
+
        if (opt->print_contents) {
                print_object_or_die(opt, data);
                batch_write(opt, "\n", 1);
>
>>
>> The rest of the changes in this file all look good to me.
>>
>>> diff --git a/t/perf/p1006-cat-file.sh b/t/perf/p1006-cat-file.sh
>>> new file mode 100755
>>> index 00000000000..e463623f5a3
>>> --- /dev/null
>>> +++ b/t/perf/p1006-cat-file.sh
>>> @@ -0,0 +1,16 @@
>>> +#!/bin/sh
>>> +
>>> +test_description='Basic sort performance tests'
>>
>> Is this description a hold-over from p0071? If so, it may be worth
>> updating here.
>>
>>> +test_expect_success 'setup' '
>>> +	git rev-list --all >rla
>>> +'
>>> +
>>> +test_perf 'cat-file --batch-check' '
>>> +	git cat-file --batch-check <rla
>>> +'
>>
>> We could probably get away with dropping the setup test and using
>> `--batch-all-objects` here. Note that right now you're only printing
>> commit objects, so there would be a slight behavior change from the way
>> the patch is currently written, but it should demonstrate the same
>> performance improvement.
>
> This sounds good to me!
>
>>
>> Thanks,
>> Taylor