Re:

From: Brandon Casey <casey@nrlssc.navy.mil>
Date: May 8, 2009, 15:51 UTC
Message-ID: <eFUCK0_CEtLa6Qvg6X1SqHmCgRnY3_3dy3OCJK26lGP-_kDRyWtlRA@cipher.nrlssc.navy.mil>
In-Reply-To: <alpine.LFD.2.01.0905080734260.4983@localhost.localdomain>

Linus Torvalds wrote:

Show 17 quoted lines

> 
> On Fri, 8 May 2009, Alex Riesen wrote:
>> I did (cygwin). My guess, the improvement is completely dwarfed by the
>> other overheads (like starting git and writing files).
> 
> Oh, I meant "git checkout" as in not even switching branches, or perhaps 
> switching branches but just changing a single file (among thousands).
> 
> If you actually end up re-writing all files, then yes, it will obviously 
> be totally dominated by other things.
> 
> For example, in the kernel, switching between two branches that only 
> differ in one file (Makefile) went from 0.18 seconds down to 0.14 seconds 
> for me just because of the fewer lstat() calls.
> 
> Noticeable? No. But it might be more noticeable on some other OS, or with 
> some networked filesystem.

plain 'git checkout' on linux kernel over NFS.

Best time without patch: 1.20 seconds

  0.45user 0.71system 0:01.20elapsed 96%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+15467minor)pagefaults 0swaps

Best time with patch (core.preloadindex = true): 1.10 seconds

  0.43user 4.00system 0:01.10elapsed 402%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+13999minor)pagefaults 0swaps

Best time with patch (core.preloadindex = false): 0.84 seconds

  0.42user 0.39system 0:00.84elapsed 96%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+13965minor)pagefaults 0swaps

Best time with read_cache_preload patch only: 1.38 seconds

  0.45user 4.42system 0:01.38elapsed 352%CPU (0avgtext+0avgdata 0maxresident)k
  0inputs+0outputs (0major+13990minor)pagefaults 0swaps

The read_cache_preload() changes actually slow things down for me for this case.

Reduction in lstat's gives a nice 30% improvement.

-brandon