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 way it just got added to gnulib too the other day.
Signed-off-by: Joachim Schmitz <jojo@schmitz-digital.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
If poll() is used as a milli-second sleep, like in help.c, by passing a NULL
in the 1st and a 0 in the 2nd arg, it exits with EFAULT.
As per Paolo Bonzini, the original author, this is a bug and to be fixed
Like in this commit, which is not to exit if the 2nd arg is 0. It got fixed
In gnulib in the same manner the other day.
Signed-off-by: Joachim Schmitz <jojo@schmitz-digital.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
In order for non-win32 platforms to be able to use poll.c, #ifdef the
inclusion of two header files properly
Signed-off-by: Joachim Schmitz <jojo@schmitz-digital.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
move poll.[ch] out of compat/win32/ into compat/poll/ and adjust
Makefile with the changed paths. Adding comments to Makefile about
how/when to enable it and add logic for this
Signed-off-by: Joachim Schmitz <jojo@schmitz-digital.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
