Re: [PATCH] Sleep 1 millisecond in poll() to avoid busy wait
Hello, On Mon, Apr 28, 2014 at 11:07:24AM +0200, Erik Faye-Lund wrote: > compat/poll/poll.c comes from Gnulib, so it would be better to submit > the patch there and update. well, the change is in gnulib since 2012-05-21. But the two versions has diverged a lot. Could you please just accept a backport of this one patch? I would be glad if msysgit could drop this patch. Updated patch follows. Stepan -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
Re: [PATCH] Sleep 1 millisecond in poll() to avoid busy wait
On Mon, Apr 28, 2014 at 10:39 AM, Stepan Kasal wrote: > From: theoleblond > Date: Wed, 16 May 2012 06:52:49 -0700 > > I played around with this quite a bit. After trying some more complex > schemes, I found that what worked best is to just sleep 1 millisecond > between iterations. Though it's a very short time, it still completely > eliminates the busy wait condition, without hurting perf. > > There code uses SleepEx(1, TRUE) to sleep. See this page for a good > discussion of why that is better than calling SwitchToThread, which > is what was used previously: > http://stackoverflow.com/questions/1383943/switchtothread-vs-sleep1 > > Note that calling SleepEx(0, TRUE) does *not* solve the busy wait. > > The most striking case was when testing on a UNC share with a large repo, > on a single CPU machine. Without the fix, it took 4 minutes 15 seconds, > and with the fix it took just 1:08! I think it's because git-upload-pack's > busy wait was eating the CPU away from the git process that's doing the > real work. With multi-proc, the timing is not much different, but tons of > CPU time is still wasted, which can be a killer on a server that needs to > do bunch of other things. > > I also tested the very fast local case, and didn't see any measurable > difference. On a big repo with 4500 files, the upload-pack took about 2 > seconds with and without the fix. > --- > > This is one of the patches that lives in msysGit, could it be > accepted upstream? > It modifies the Windows compat function only. compat/poll/poll.c comes from Gnulib, so it would be better to submit the patch there and update. -- To unsubscribe from this list: send the line "unsubscribe git" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
[PATCH] Sleep 1 millisecond in poll() to avoid busy wait
From: theoleblond
Date: Wed, 16 May 2012 06:52:49 -0700
I played around with this quite a bit. After trying some more complex
schemes, I found that what worked best is to just sleep 1 millisecond
between iterations. Though it's a very short time, it still completely
eliminates the busy wait condition, without hurting perf.
There code uses SleepEx(1, TRUE) to sleep. See this page for a good
discussion of why that is better than calling SwitchToThread, which
is what was used previously:
http://stackoverflow.com/questions/1383943/switchtothread-vs-sleep1
Note that calling SleepEx(0, TRUE) does *not* solve the busy wait.
The most striking case was when testing on a UNC share with a large repo,
on a single CPU machine. Without the fix, it took 4 minutes 15 seconds,
and with the fix it took just 1:08! I think it's because git-upload-pack's
busy wait was eating the CPU away from the git process that's doing the
real work. With multi-proc, the timing is not much different, but tons of
CPU time is still wasted, which can be a killer on a server that needs to
do bunch of other things.
I also tested the very fast local case, and didn't see any measurable
difference. On a big repo with 4500 files, the upload-pack took about 2
seconds with and without the fix.
---
This is one of the patches that lives in msysGit, could it be
accepted upstream?
It modifies the Windows compat function only.
Have a nice day,
Stepan
compat/poll/poll.c | 4 +++-
1 file changed, 3 insertions(+), 1 deletion(-)
diff --git a/compat/poll/poll.c b/compat/poll/poll.c
index 31163f2..c5a9a93 100644
--- a/compat/poll/poll.c
+++ b/compat/poll/poll.c
@@ -605,7 +605,9 @@ restart:
if (!rc && timeout == INFTIM)
{
- SwitchToThread();
+ /* Sleep 1 millisecond to avoid busy wait */
+ SleepEx(1, TRUE);
+
goto restart;
}
--
1.9.2.msysgit.0.158.g6070cee
--
To unsubscribe from this list: send the line "unsubscribe git" in
the body of a message to majord...@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
