Re: Git performance on OS X

From: Linus Torvalds <torvalds@linux-foundation.org>
Date: Apr 19, 2008, 23:26 UTC
Message-ID: <alpine.LFD.1.10.0804191619240.2779@woody.linux-foundation.org>
In-Reply-To: <0BE9BBE3-EA9D-4A66-A086-A2A1B289B0DD@ai.rug.nl>

On Sun, 20 Apr 2008, Pieter de Bie wrote:

> 
> The number of lstats are cut down by your patch: 428761 vs. 338091. Funnily
> enough, there is no significant difference in run-time:

It may be that the problem with OS X is a sucky pathname cache mechanism.

The trivial patch cut down the number of stat() calls by a fair amount, but the calls that got removed were all of the "do two 'lstat()' calls on the exact same pathname consecutively" type.

Maybe OS X has some very limited pathname caching that catches that, or even if not, it just ends up being very nice in the D$, so it's not a big deal. And then the real suckiness happens only with bigger workloads.

It may also be that the bulk of the OS X cost isn't in lstat() at all, but in the VM. That was true for some other OS X load.

> Command                                            Mean     Std
> git status .                                       13.970  1.298
> /Users/pieter/projects/External/git/git-status .   13.759  0.321

This is the WebKit archive, right?

For me, doing a "time git status ." on the WebKit thing I just cloned from git://git.webkit.org/WebKit.git is much faster: 1.264s (and it goes down by maybe 5-10% with my lstat-avoidance patch).

Is there any system-level profiler for OS X to get a clue where that cost is, in case it's not the lstat() at all?

			Linus