From: Jacob Vosmaer <jacob@gitlab.com>
To: Jeff King <peff@peff.net>
Cc: Junio C Hamano <gitster@pobox.com>, Taylor Blau <me@ttaylorr.com>,
Git Mailing List <git@vger.kernel.org>,
ps@pks.im
Subject: Re: [PATCH v3 0/2] send_ref buffering
Date: Tue, 31 Aug 2021 15:08:25 +0200 [thread overview]
Message-ID: <CADMWQoPerffQcTfKh3bfesjgHaBqXGzW2805knyRW3R_q4V-YA@mail.gmail.com> (raw)
In-Reply-To: <YS4DmlJdjxeo+QI0@coredump.intra.peff.net>
On Tue, Aug 31, 2021 at 12:25 PM Jeff King <peff@peff.net> wrote:
> I do think it would be nice to take the packet_writer
> interface further (letting it replace the static buf, and use stdio
> handles, and using it throughout upload-pack).
I would like that too, for the sake of neatness and general
performance, but I don't have the time to take on a larger project
like that at the moment.
> Does the 64k buffer actually improve things? Here are the timings I get
> on a repo with ~1M refs (it's linux.git with one ref per commit).
Thanks for challenging that. I have a repeatable benchmark where it
matters, because each write syscall wakes up a chain of proxies
between the user and git-upload-pack. Larger buffers means fewer
wake-ups. But then I tried to simplify my example by having sshd as
the only intermediary, and in that experiment 64K buffers were not
better than 4K buffers. I think that goes to show that picking a good
buffer size is hard, and we'd be better off picking one specifically
for Gitaly (and GitLab) that works with our stack.
> Summary
> 'GIT_REF_PARANOIA=1 git.compile upload-pack .' ran
> 2.17 ± 0.02 times faster than 'git.compile upload-pack .'
>
> It's not exactly the intended use of that environment variable, but its
> side effect is that we do not call has_object_file() on each ref tip.
That is nice to know, but as a user of Git I don't know when it is or
is not safe to skip those has_object_file() calls. If it's safe to
skip them then Git should skip them always. If not, then I will err on
the side of caution and keep the checks.
Jacob
next prev parent reply other threads:[~2021-08-31 13:08 UTC|newest]
Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-24 14:02 [PATCH 1/1] upload-pack: buffer ref advertisement writes Jacob Vosmaer
2021-08-24 21:07 ` Taylor Blau
2021-08-24 21:42 ` Junio C Hamano
2021-08-25 0:44 ` Jeff King
2021-08-26 10:02 ` Jacob Vosmaer
2021-08-26 10:06 ` [PATCH 1/2] pkt-line: add packet_fwrite Jacob Vosmaer
2021-08-26 10:06 ` [PATCH 2/2] upload-pack: use stdio in send_ref callbacks Jacob Vosmaer
2021-08-26 16:33 ` Junio C Hamano
2021-08-26 20:21 ` Junio C Hamano
2021-08-26 22:35 ` Taylor Blau
2021-08-26 23:24 ` Jeff King
2021-08-27 16:15 ` Junio C Hamano
2021-08-31 9:34 ` [PATCH v3 0/2] send_ref buffering Jacob Vosmaer
2021-08-31 9:34 ` [PATCH v3 1/2] pkt-line: add stdio packet write functions Jacob Vosmaer
2021-08-31 10:37 ` Jeff King
2021-08-31 18:13 ` Junio C Hamano
2021-09-01 12:54 ` [PATCH v4 0/2] send_ref buffering Jacob Vosmaer
2021-09-01 12:54 ` [PATCH v4 1/2] pkt-line: add stdio packet write functions Jacob Vosmaer
2021-09-01 12:54 ` [PATCH v4 2/2] upload-pack: use stdio in send_ref callbacks Jacob Vosmaer
2021-09-02 9:18 ` [PATCH v4 0/2] send_ref buffering Jeff King
2021-08-31 9:34 ` [PATCH v3 2/2] upload-pack: use stdio in send_ref callbacks Jacob Vosmaer
2021-08-31 10:25 ` [PATCH v3 0/2] send_ref buffering Jeff King
2021-08-31 13:08 ` Jacob Vosmaer [this message]
2021-08-31 17:44 ` Jacob Vosmaer
2021-09-01 0:15 ` Jeff King
2021-08-26 23:32 ` [PATCH 2/2] upload-pack: use stdio in send_ref callbacks Jeff King
2021-08-26 16:33 ` [PATCH 1/2] pkt-line: add packet_fwrite Junio C Hamano
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