From: Junio C Hamano <gitster@pobox.com>
Date: Wed, 24 May 2017 04:45:32 GMT
Subject: Re: [PATCH v2 2/7] grep: skip pthreads overhead when using one thread
Message-ID: <xmqqr2zehngz.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170523192453.14172-3-avarab@gmail.com>

Ævar Arnfjörð Bjarmason  <avarab@gmail.com> writes:

> Skip the administrative overhead of using pthreads when only using one
> thread. Instead take the non-threaded path which would be taken under
> NO_PTHREADS.
>
> The threading support was initially added in commit
> 5b594f457a ("Threaded grep", 2010-01-25) with a hardcoded compile-time
> number of 8 threads. Later the number of threads was made configurable
> in commit 89f09dd34e ("grep: add --threads=<num> option and
> grep.threads configuration", 2015-12-15).
>
> That change did not add any special handling for --threads=1. Now we
> take a slightly faster path by skipping thread handling entirely when
> 1 thread is requested.

OK, this is what Peff and you were discussing in the earlier round,
having the controller do the work himself, instead of sitting and
waiting for a sole worker to finish the work.  Looks good.

Thanks.

>
> Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
> ---
>  builtin/grep.c | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/builtin/grep.c b/builtin/grep.c
> index 12e62fcbf3..bd008cb100 100644
> --- a/builtin/grep.c
> +++ b/builtin/grep.c
> @@ -1238,6 +1238,8 @@ int cmd_grep(int argc, const char **argv, const char *prefix)
>  		num_threads = GREP_NUM_THREADS_DEFAULT;
>  	else if (num_threads < 0)
>  		die(_("invalid number of threads specified (%d)"), num_threads);
> +	if (num_threads == 1)
> +		num_threads = 0;
>  #else
>  	if (num_threads)
>  		warning(_("no threads support, ignoring --threads"));