From: Jeff King <peff@peff.net>
Date: Tue, 22 May 2012 17:34:48 GMT
Subject: Re: [PATCH] find_containing_dir(): allocate strbuf less extravagantly
Message-ID: <20120522173448.GD11600@sigill.intra.peff.net>
In-Reply-To: <1337692566-3718-1-git-send-email-mhagger@alum.mit.edu>

On Tue, May 22, 2012 at 03:16:06PM +0200, mhagger@alum.mit.edu wrote:

> From: Michael Haggerty <mhagger@alum.mit.edu>
> 
> It might seem like allocating a fixed-length buffer of uninitialized
> memory should be pretty cheap even if the buffer is of size PATH_MAX.
> But empirically, it is measurably faster to allocated only the strlen
> of the input string.
> 
> Thanks to Peff for pointing out a performance regression in this area
> that might be fixed by this patch.
> 
> Signed-off-by: Michael Haggerty <mhagger@alum.mit.edu>
> ---
> I am not able to reproduce performance regressions as bad as those
> observed by Peff.  It seems to depend on the amount of memory
> pressure.  The smaller regression that I *did* see is fixed by this
> patch, reducing the time for "git fetch . refs/*:refs/*" from 10.1 s
> to 9.3 s.  The change is sensible in any case, but we will have to
> wait for Peff's verdict about whether it fixes the whole problem for
> him, too.

I see a similar small improvement. So I think it is worth doing, but it
does not fix the main regression I found.

-Peff