From: Junio C Hamano <gitster@pobox.com>
To: Jeff King <peff@peff.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Johannes Schindelin <Johannes.Schindelin@gmx.de>,
Git Mailing List <git@vger.kernel.org>,
Lars Schneider <larsxschneider@gmail.com>,
Eric Wong <e@80x24.org>
Subject: Re: [PATCH v3 2/3] sha1_file: open window into packfiles with O_CLOEXEC
Date: Mon, 31 Oct 2016 10:55:32 -0700 [thread overview]
Message-ID: <xmqqwpgotncb.fsf@gitster.mtv.corp.google.com> (raw)
In-Reply-To: <20161031135601.7immbp44wn7uksvs@sigill.intra.peff.net> (Jeff King's message of "Mon, 31 Oct 2016 09:56:01 -0400")
Jeff King <peff@peff.net> writes:
> If you set a probe on touch_atime() in the kernel (which is called for
> every attempt to smudge the atime, regardless of mount options, but is
> skipped when the descriptor was opened with O_NOATIME), you can see the
> impact. Here's a command I picked because it reads a lot of objects (run
> on my git.git clone):
>
> $ perf stat -e probe:touch-atime git log -Sfoo >/dev/null
>
> And the probe:touch_atime counts before (stock git) and after (a patch
> to drop O_NOATIME):
>
> before: 22,235
> after: 22,362
>
> So that's only half a percent difference. And it's on a reasonably messy
> clone that is partway to triggering an auto-repack:
> ...
> So I guess it's possible that it produces a noticeable effect in some
> cases, but I'm still somewhat doubtful. And actually repacking your
> repository had a greater effect in every case I measured (in addition to
> providing other speedups).
Let's keep doubting. I prefer one-step-at-a-time approach to
things anyway, and what I plan in the near term are:
* use the "open() with O_NOATIME|O_CLOEXEC, gradually losing the
bits during fallback" approach in the ls/git-open-cloexec topic,
in order to help ls/filter-process topic be part of the upcoming
release;
* simplify the logic to the "open(2) with O_CLOEXEC, set O_NOATIME
with fcntl(2)" in jc/git-open-cloexec~1 after 2.11 ships;
* cook "drop the latter half of setting O_NOATIME" which is at the
tip of jc/git-open-cloexec in 'next', and while Linus is looking
the other way ^W^W^W^W^W^W^W after people had chance to complain
with numbers, merge it to a future release iff it still looked OK
to drop O_NOATIME thing.
next prev parent reply other threads:[~2016-10-31 17:56 UTC|newest]
Thread overview: 54+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-24 18:02 [PATCH v2 0/2] Use CLOEXEC to avoid fd leaks larsxschneider
2016-10-24 18:02 ` [PATCH v2 1/2] sha1_file: open window into packfiles with CLOEXEC larsxschneider
2016-10-25 10:27 ` Johannes Schindelin
2016-10-25 16:58 ` Junio C Hamano
2016-10-24 18:03 ` [PATCH v2 2/2] read-cache: make sure file handles are not inherited by child processes larsxschneider
2016-10-24 18:39 ` Eric Wong
2016-10-24 19:53 ` Junio C Hamano
2016-10-25 10:33 ` Johannes Schindelin
2016-10-25 17:02 ` Junio C Hamano
2016-10-24 19:22 ` Johannes Sixt
2016-10-24 19:53 ` Lars Schneider
2016-10-25 21:39 ` Johannes Sixt
2016-10-24 18:23 ` [PATCH v2 0/2] Use CLOEXEC to avoid fd leaks Junio C Hamano
2016-10-25 11:27 ` Johannes Schindelin
2016-10-25 18:16 ` [PATCH v3 0/3] quick reroll of Lars's git_open() w/ O_CLOEXEC Junio C Hamano
2016-10-25 18:16 ` [PATCH v3 1/3] sha1_file: rename git_open_noatime() to git_open() Junio C Hamano
2016-10-25 18:16 ` [PATCH v3 2/3] sha1_file: open window into packfiles with O_CLOEXEC Junio C Hamano
2016-10-26 4:25 ` Jeff King
2016-10-26 16:23 ` Junio C Hamano
2016-10-26 16:47 ` Jeff King
2016-10-26 17:52 ` Junio C Hamano
2016-10-26 20:17 ` Jeff King
2016-10-26 21:15 ` Junio C Hamano
2016-10-27 10:24 ` Jeff King
2016-10-27 21:49 ` Junio C Hamano
2016-10-27 22:38 ` Linus Torvalds
2016-10-27 22:56 ` Junio C Hamano
2016-10-27 23:09 ` Linus Torvalds
2016-10-27 23:19 ` Linus Torvalds
2016-10-27 23:36 ` Junio C Hamano
2016-10-27 23:44 ` Linus Torvalds
2016-10-28 1:08 ` Junio C Hamano
2016-10-28 2:37 ` Junio C Hamano
2016-10-28 5:51 ` Eric Wong
2016-10-28 11:11 ` Johannes Schindelin
2016-10-28 16:13 ` Linus Torvalds
2016-10-28 16:48 ` Junio C Hamano
2016-10-28 17:38 ` Linus Torvalds
2016-10-28 17:47 ` Junio C Hamano
2016-10-29 1:26 ` Junio C Hamano
2016-10-29 8:25 ` Johannes Schindelin
2016-10-29 17:06 ` Linus Torvalds
2016-10-31 17:37 ` Junio C Hamano
2016-10-31 13:56 ` Jeff King
2016-10-31 17:55 ` Junio C Hamano [this message]
2016-10-31 18:05 ` Jeff King
2016-10-28 13:32 ` Junio C Hamano
2016-10-28 13:33 ` Junio C Hamano
2016-10-28 7:51 ` Jeff King
2016-10-25 18:16 ` [PATCH v3 3/3] read-cache: make sure file handles are not inherited by child processes Junio C Hamano
2016-10-25 21:33 ` Eric Wong
2016-10-25 22:54 ` Junio C Hamano
2016-10-25 21:48 ` [PATCH v3 0/3] quick reroll of Lars's git_open() w/ O_CLOEXEC Lars Schneider
2016-10-25 22:56 ` Junio C Hamano
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