From: Jeff King <peff@peff.net>
To: "Ævar Arnfjörð Bjarmason" <avarab@gmail.com>
Cc: "Git Mailing List" <git@vger.kernel.org>,
"Junio C Hamano" <gitster@pobox.com>,
"Jeffrey Walton" <noloader@gmail.com>,
"Michał Kiedrowicz" <michal.kiedrowicz@gmail.com>,
"J Smith" <dark.panda@gmail.com>,
"Victor Leschuk" <vleschuk@gmail.com>,
"Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>,
"Thomas Rast" <trast@student.ethz.ch>,
"Fredrik Kuivinen" <frekui@gmail.com>
Subject: Re: [PATCH 01/12] grep: add ability to disable threading with --threads=0 or grep.threads=0
Date: Tue, 11 Apr 2017 16:34:34 -0400 [thread overview]
Message-ID: <20170411203434.iiupo2oovzviqju5@sigill.intra.peff.net> (raw)
In-Reply-To: <CACBZZX7vEQ5jUzX3GsD6JXe50TnRUtGmSVi7zBxwOmAQGABQ4Q@mail.gmail.com>
On Tue, Apr 11, 2017 at 10:20:59PM +0200, Ævar Arnfjörð Bjarmason wrote:
> I'm struggling to find a use-case where threading makes sense at all.
> The example in the initial introduction in 5b594f457a is always slower
> with >0 for me, and since then in 0579f91dd7 it got disabled entirely
> for non-worktree cases.
It's a big win for me in worktree greps of linux.git:
$ best-of-five git grep --threads=1 '[q]werty'
Attempt 1: 0.713
Attempt 2: 0.708
Attempt 3: 0.689
Attempt 4: 0.695
Attempt 5: 0.7
real 0m0.689s
user 0m0.560s
sys 0m0.248s
$ best-of-five git grep --threads=8 '[q]werty'
Attempt 1: 0.238
Attempt 2: 0.225
Attempt 3: 0.222
Attempt 4: 0.221
Attempt 5: 0.225
real 0m0.221s
user 0m0.936s
sys 0m0.356s
In non-worktree cases most of the time goes to accessing objects, which
happens under a lock. So you don't get any real parallelism, just
overhead.
> But assuming it works for someone out there, then 0 threads is clearly
> not the same as 1. On linux.git with pcre2 grepping for [q]werty for
> example[1]
Right, my suggestion was to teach "grep" to treat --threads=1 as "do not
spawn any other threads". I.e., to make it like the "0" case you were
proposing, and then leave "0" as "auto-detect". There would be no way to
spawn a _single_ thread and feed it. But why would you want to do that?
It's always going to be strictly worse than not threading at all.
-Peff
next prev parent reply other threads:[~2017-04-11 20:34 UTC|newest]
Thread overview: 43+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-04-08 13:24 [PATCH 00/12] PCREv2 & more Ævar Arnfjörð Bjarmason
2017-04-08 13:24 ` [PATCH 01/12] grep: add ability to disable threading with --threads=0 or grep.threads=0 Ævar Arnfjörð Bjarmason
2017-04-11 10:06 ` Jeff King
2017-04-11 20:20 ` Ævar Arnfjörð Bjarmason
2017-04-11 20:34 ` Jeff King [this message]
2017-04-11 20:56 ` Ævar Arnfjörð Bjarmason
2017-04-14 21:23 ` Jeff King
2017-04-16 22:25 ` Ævar Arnfjörð Bjarmason
2017-04-08 13:24 ` [PATCH 02/12] grep: remove redundant regflags assignment under PCRE Ævar Arnfjörð Bjarmason
2017-04-11 10:10 ` Jeff King
2017-04-08 13:24 ` [PATCH 03/12] Makefile & configure: reword outdated comment about PCRE Ævar Arnfjörð Bjarmason
2017-04-11 10:14 ` Jeff King
2017-04-15 12:10 ` Ævar Arnfjörð Bjarmason
2017-04-08 13:24 ` [PATCH 04/12] grep: add a test for backreferences in PCRE patterns Ævar Arnfjörð Bjarmason
2017-04-08 13:24 ` [PATCH 05/12] log: add exhaustive tests for pattern style options & config Ævar Arnfjörð Bjarmason
2017-04-11 10:23 ` Jeff King
2017-04-11 10:32 ` Ævar Arnfjörð Bjarmason
2017-04-11 10:51 ` Jeff King
2017-04-08 13:25 ` [PATCH 06/12] log: add -P as a synonym for --perl-regexp Ævar Arnfjörð Bjarmason
2017-04-10 2:39 ` Junio C Hamano
2017-04-11 10:26 ` Jeff King
2017-04-08 13:25 ` [PATCH 07/12] grep & rev-list doc: stop promising libpcre " Ævar Arnfjörð Bjarmason
2017-04-08 13:25 ` [PATCH 08/12] grep: make grep.patternType=[pcre|pcre1] a synonym for "perl" Ævar Arnfjörð Bjarmason
2017-04-11 10:30 ` Jeff King
2017-04-08 13:25 ` [PATCH 09/12] test-lib: rename the LIBPCRE prerequisite to PCRE Ævar Arnfjörð Bjarmason
2017-04-11 10:31 ` Jeff King
2017-04-08 13:25 ` [PATCH 10/12] grep: change the internal PCRE macro names to be PCRE1 Ævar Arnfjörð Bjarmason
2017-04-11 10:35 ` Jeff King
2017-04-11 10:51 ` Ævar Arnfjörð Bjarmason
2017-04-11 10:53 ` Jeff King
2017-04-08 13:25 ` [PATCH 11/12] grep: change the internal PCRE code & header " Ævar Arnfjörð Bjarmason
2017-04-11 10:37 ` Jeff King
2017-04-11 10:45 ` Ævar Arnfjörð Bjarmason
2017-04-11 10:48 ` Jeff King
2017-04-11 11:02 ` Ævar Arnfjörð Bjarmason
2017-04-11 12:57 ` Jeff King
2017-04-11 16:51 ` Brandon Williams
2017-04-11 18:31 ` Ævar Arnfjörð Bjarmason
2017-04-08 13:25 ` [PATCH 12/12] grep: add support for PCRE v2 Ævar Arnfjörð Bjarmason
2017-04-11 10:43 ` Jeff King
2017-04-11 10:47 ` [PATCH 00/12] PCREv2 & more Jeff King
2017-04-15 8:11 ` Junio C Hamano
2017-04-15 9:50 ` Ævar Arnfjörð Bjarmason
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