From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: Sun, 25 Dec 2011 03:32:27 GMT
Subject: Re: [PATCH v2 3/3] grep: disable threading in all but worktree case
Message-ID: <CACsJy8AU+a6bHa4qGX0eYgdnP6+PhP7q0pty+bHLBupwr9LCMw@mail.gmail.com>
In-Reply-To: <20111224070715.GA32267@sigill.intra.peff.net>

On Sat, Dec 24, 2011 at 2:07 PM, Jeff King <peff@peff.net> wrote:
> The case where we would most expect the setup cost to be drowned out is
> using a more complex regex, grepping tree objects. There we have a
> baseline of:
>
>  $ time git grep 'a.*c' HEAD >/dev/null
>  real    0m5.684s
>  user    0m5.472s
>  sys     0m0.196s
>
>  $ time git ls-tree --name-only -r HEAD |
>      xargs git grep 'a.*c' HEAD -- >/dev/null
>  real    0m10.906s
>  user    0m10.725s
>  sys     0m0.240s
>
> Here, we still almost double our time. It looks like we don't use the
> same pathspec matching code in this case. But we do waste a lot of extra
> time zlib-inflating the trees in "ls-tree", only to do it separately in
> "grep".

Or you could pass blob SHA-1 to git grep to avoid reinflating trees

$ time git ls-tree -r HEAD|cut -c 13-52|xargs git grep 'a.*c' >/dev/null

Doing it in parallel does not seem to save time for me though.
-- 
Duy