From: Linus Torvalds <torvalds@osdl.org>
To: Marco Costalba <mcostalba@gmail.com>
Cc: Git Mailing List <git@vger.kernel.org>,
Junio C Hamano <junkio@cox.net>, Alex Riesen <raa.lkml@gmail.com>,
Shawn Pearce <spearce@spearce.org>
Subject: Re: [RFC \ WISH] Add -o option to git-rev-list
Date: Sun, 10 Dec 2006 14:53:43 -0800 (PST) [thread overview]
Message-ID: <Pine.LNX.4.64.0612101439540.12500@woody.osdl.org> (raw)
In-Reply-To: <e5bfff550612101435o6bc938acmac28ad6adf0c8844@mail.gmail.com>
On Sun, 10 Dec 2006, Marco Costalba wrote:
>
> I consistently have len == 65536 bytes until the last fread() where
> it's less.
That's because fread() will block until it gets all data. Did you actually
ever try this with a uncached tree and did you compare what you got with a
plain "read()".
On older kernels, I guarantee that you get 4kB at a time for reads, even
for a blocking pipe. Because we have bigger pipe buffers these days, it
_may_ return 64kB at a time every time, but only if the writer is much
faster than the reader.
Based on the fact that you say that "read()" was ten times slower than
fread(), I very much suspect you got 4kB at a time, and then slept 100ms
each time or something.
Anyway, you should seriously also check the case when "git rev-list" is
slow because you have cold caches and unpacked objects. You can't wait for
it to synchronously write a thousand lines or so - that could take
seconds.
> How can open in nonblocking mode with popen() ?
>
> FILE *popen(const char *command, const char *type);
something like
fcntl(fileno(file), F_SETFL, O_NONBLOCK);
will do it, and then your loop should look something like
for (;;) {
int count = read(fileno(file), buf, BUFSIZE);
if (!count) {
/* All done, no more to read */
return 0;
}
if (count < 0) {
if (errno == EAGAIN)
break;
if (errno == EINTR)
continue;
/* Anything else is fatal - report error */
return -1;
}
... handle 'count' new bytes here ...
}
.. this is the EAGAIN case ..
either set polling on the file descriptor, or use a
timer here yo get back to this loop eventually.
looks about right.
next prev parent reply other threads:[~2006-12-10 22:53 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2006-12-10 11:38 [RFC \ WISH] Add -o option to git-rev-list Marco Costalba
2006-12-10 14:54 ` Alex Riesen
2006-12-10 18:16 ` Linus Torvalds
2006-12-10 19:51 ` Marco Costalba
2006-12-10 20:00 ` globs in partial checkout? Michael S. Tsirkin
2006-12-10 20:13 ` Linus Torvalds
2006-12-10 21:07 ` Michael S. Tsirkin
2006-12-10 20:08 ` [RFC \ WISH] Add -o option to git-rev-list Linus Torvalds
2006-12-10 20:19 ` Linus Torvalds
2006-12-10 22:05 ` Marco Costalba
2006-12-10 22:09 ` Marco Costalba
2006-12-10 22:16 ` Linus Torvalds
2006-12-10 22:35 ` Marco Costalba
2006-12-10 22:53 ` Linus Torvalds [this message]
2006-12-11 0:15 ` Marco Costalba
2006-12-11 0:51 ` Linus Torvalds
2006-12-11 7:17 ` Marco Costalba
2006-12-11 10:00 ` Alex Riesen
2006-12-11 16:59 ` Linus Torvalds
2006-12-11 17:07 ` Linus Torvalds
2006-12-11 17:39 ` Marco Costalba
2006-12-11 18:15 ` Linus Torvalds
2006-12-11 18:59 ` Marco Costalba
2006-12-11 19:25 ` Linus Torvalds
2006-12-11 20:28 ` Josef Weidendorfer
2006-12-11 20:40 ` Linus Torvalds
2006-12-11 20:54 ` Josef Weidendorfer
2006-12-11 21:14 ` Linus Torvalds
2006-12-15 18:45 ` Marco Costalba
2006-12-15 19:20 ` Linus Torvalds
2006-12-15 20:41 ` Marco Costalba
2006-12-15 21:04 ` Marco Costalba
2006-12-11 9:26 ` Josef Weidendorfer
2006-12-11 12:52 ` Marco Costalba
2006-12-11 13:28 ` Josef Weidendorfer
2006-12-11 17:28 ` Marco Costalba
2006-12-11 11:39 ` Andreas Ericsson
2006-12-11 12:59 ` Marco Costalba
2006-12-11 13:40 ` Andreas Ericsson
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