Re: [PATCH] Improving performance with pthreads in refresh_index().

klinkert@webgods.de venit, vidit, dixit 11.10.2011 11:32:

Git performs for every file in a repository at least one (with a cold cache)
lstat(). In larger repositories operations like git status take a
long time. In case your local repository is located on a remote server
(e. g. mounted via nfs) it ends up in an *incredible* slow git.

With this patch you're able to determine a number of threads (maxthreads)
in your config file to run these tons of lstats in threads. There
won't be created any pthreads if you haven't set maxthreads. In my
test cases a git status with this patch performs enormously faster (over
two minutes before and approximately 25 seconds now). Of course, it
has a positive impact on other git commands, too.

Can you specify under which circumstances one should get a speedup? Our
NFS isn't slow enough... but on a dead slow sshfs work tree I get the
following for "git status -s":

maxthreads: 0, preloadindex: false, time: 14.73
maxthreads: 1, preloadindex: false, time: 14.25
maxthreads: 2, preloadindex: false, time: 13.32
maxthreads: 3, preloadindex: false, time: 12.40
maxthreads: 4, preloadindex: false, time: 12.65
maxthreads: 5, preloadindex: false, time: 12.16
maxthreads: 8, preloadindex: false, time: 12.32
maxthreads: 10, preloadindex: false, time: 11.98
maxthreads: 15, preloadindex: false, time: 12.31
maxthreads: 20, preloadindex: false, time: 12.00
maxthreads: 0, preloadindex: true, time: 12.17
maxthreads: 1, preloadindex: true, time: 11.98
maxthreads: 2, preloadindex: true, time: 12.21
maxthreads: 3, preloadindex: true, time: 11.99
maxthreads: 4, preloadindex: true, time: 12.14
maxthreads: 5, preloadindex: true, time: 12.21
maxthreads: 8, preloadindex: true, time: 12.14
maxthreads: 10, preloadindex: true, time: 12.08
maxthreads: 15, preloadindex: true, time: 12.16
maxthreads: 20, preloadindex: true, time: 11.96

So it seams it gives me what preloadindex does, which is not much.

Note: I'm not saying the patch is bad. I'm just wondering whether that
is expected.

Michael
P.S.: It's actually sshfs with ssh to an NFSv3 client (server restricts
exports) :(