From: Jeff King <peff@peff.net>
Date: Wed, 07 Dec 2011 04:24:31 GMT
Subject: Re: [PATCH v2 3/3] grep: disable threading in all but worktree case
Message-ID: <20111207042431.GA10765@sigill.intra.peff.net>
In-Reply-To: <4EDE9BBA.2010409@lsrfire.ath.cx>

On Tue, Dec 06, 2011 at 11:48:26PM +0100, René Scharfe wrote:

>  #ifndef NO_PTHREADS
> -	if (use_threads) {
> +	if (nr_threads > 0) {
>  		grep_sha1_async(opt, name, sha1);
>  		return 0;
>  	} else

Should this be "if (nr_threads > 1)"?

As a user, I would do:

  git grep --threads=1 ...

if I wanted a single-threaded process. Instead, we actually spawn a
sub-thread and do all of the locking, which has a measurable cost:

  $ time git grep --threads=0 SIMPLE HEAD >/dev/null
  real    0m2.994s
  user    0m2.932s
  sys     0m0.060s

  $ time git grep --threads=1 SIMPLE HEAD >/dev/null
  real    0m3.407s
  user    0m3.392s
  sys     0m0.140s

Should --threads=1 be equivalent to --threads=0?

-Peff