Re: [PATCH v2 10/13] bash prompt: combine 'git rev-parse' executions

From: Jeff King <peff@peff.net>
Date: Jun 18, 2013, 06:05 UTC
Message-ID: <20130618060535.GE5916@sigill.intra.peff.net>
In-Reply-To: <1371521826-3225-11-git-send-email-szeder@ira.uka.de>

On Tue, Jun 18, 2013 at 04:17:03AM +0200, SZEDER Gábor wrote:

Show 30 quoted lines

> The whole series speeds up the bash prompt on Windows/MSysGit
> considerably.  Here are some timing results in two scenarios, repeated
> 10 times:
> 
> At the top of the work tree, before:
> 
>     $ time for i in {0..9} ; do prompt="$(__git_ps1)" ; done
> 
>     real    0m1.716s
>     user    0m0.301s
>     sys     0m0.772s
> 
>   After:
> 
>     real    0m0.686s
>     user    0m0.075s
>     sys     0m0.287s
> 
> In a subdirectory, during rebase, stash status indicator enabled,
> before:
> 
>     real    0m3.557s
>     user    0m0.495s
>     sys     0m1.767s
> 
>   After:
> 
>     real    0m0.702s
>     user    0m0.045s
>     sys     0m0.409s

Very nice speedup (or perhaps it is a testament to how bad fork() is on msys). Reading patches 8 and 9, I can't help but feel that "git status" is letting us down a little by making us parse all of this data ourselves. In theory, __git_ps1() could just be something like:

  eval "$(git status --shell)"
  printf ...

and the heavy lifting could be done in a single C process which does not have to worry about fork overhead. But that is quite far from where we are now, so while it might be an interesting place to go in the future, I do not think such dreams would want to hold up current work.

-Peff