git.vger.kernel.org archive mirror
 help / color / mirror / Atom feed
From: Eric Sunshine <sunshine@sunshineco.com>
To: Jeff King <peff@peff.net>
Cc: "Eric Wong" <e@80x24.org>,
	"Eric Sunshine via GitGitGadget" <gitgitgadget@gmail.com>,
	"Git List" <git@vger.kernel.org>,
	"Elijah Newren" <newren@gmail.com>,
	"Ævar Arnfjörð Bjarmason" <avarab@gmail.com>,
	"Fabian Stelzer" <fs@gigacodes.de>,
	"Johannes Schindelin" <Johannes.Schindelin@gmx.de>
Subject: Re: [PATCH 06/18] chainlint.pl: validate test scripts in parallel
Date: Sun, 20 Nov 2022 23:02:54 -0500	[thread overview]
Message-ID: <CAPig+cTge7kp9bH+Xd8wpqmEZuuEFE0xQdgqaFP1WAQ-F+xyHA@mail.gmail.com> (raw)
In-Reply-To: <YxfXQ0IJjq/FT2Uh@coredump.intra.peff.net>

On Tue, Sep 6, 2022 at 7:27 PM Jeff King <peff@peff.net> wrote:
> I did some timings the other night, and I found something quite curious
> with the thread stuff.
>
> I was quite surprised that it made things slower! It's nice that we're
> only calling it once per script instead of once per test, but it seems
> the startup overhead of the script is really high.
>
> And since in this mode we're only feeding it one script at a time, I
> tried reverting the "chainlint.pl: validate test scripts in parallel"
> commit. And indeed, now things are much faster:
>
>   Benchmark 1: make
>     Time (mean ± σ):     61.544 s ±  3.364 s    [User: 556.486 s, System: 384.001 s]
>     Range (min … max):   57.660 s … 63.490 s    3 runs
>
> And you can see the same thing just running chainlint by itself:
>
>   $ time perl chainlint.pl /dev/null
>   real  0m0.069s
>   user  0m0.042s
>   sys   0m0.020s
>
>   $ git revert HEAD^{/validate.test.scripts.in.parallel}
>   $ time perl chainlint.pl /dev/null
>   real  0m0.014s
>   user  0m0.010s
>   sys   0m0.004s
>
> I didn't track down the source of the slowness. Maybe it's loading extra
> modules, or maybe it's opening /proc/cpuinfo, or maybe it's the thread
> setup. But it's a surprising slowdown.

It is surprising, and unfortunate. Ditching "ithreads" would probably
be a good idea. (more on that below)

> Now of course your intent is to do a single repo-wide invocation. And
> that is indeed a bit faster. Here it is without the parallel code:
>
>   Benchmark 1: make
>     Time (mean ± σ):     61.727 s ±  2.140 s    [User: 507.712 s, System: 377.753 s]
>     Range (min … max):   59.259 s … 63.074 s    3 runs
>
> The wall-clock time didn't improve much, but the CPU time did. Restoring
> the parallel code does improve the wall-clock time a bit, but at the
> cost of some extra CPU:
>
>   Benchmark 1: make
>     Time (mean ± σ):     59.029 s ±  2.851 s    [User: 515.690 s, System: 380.369 s]
>     Range (min … max):   55.736 s … 60.693 s    3 runs
>
> which makes sense. If I do a with/without of just "make test-chainlint",
> the parallelism is buying a few seconds of wall-clock:
>
>   Benchmark 1: make test-chainlint
>     Time (mean ± σ):     900.1 ms ± 102.9 ms    [User: 12049.8 ms, System: 79.7 ms]
>     Range (min … max):   704.2 ms … 994.4 ms    10 runs
>
>   Benchmark 1: make test-chainlint
>     Time (mean ± σ):      3.778 s ±  0.042 s    [User: 3.756 s, System: 0.023 s]
>     Range (min … max):    3.706 s …  3.833 s    10 runs
>
> I'm not sure what it all means. For Linux, I think I'd be just as happy
> with a single non-parallelized test-chainlint run for each file. But
> maybe on Windows the startup overhead is worse? OTOH, the whole test run
> is so much worse there. One process per script is not going to be that
> much in relative terms either way.

Somehow Windows manages to be unbelievably slow no matter what. I
mentioned elsewhere (after you sent this) that I tested on a five or
six year old 8-core dual-boot machine. Booted to Linux, running a
single chainlint.pl invocation using all 8 cores to check all scripts
in the project took under 1 second walltime. The same machine booted
to Windows using all 8 cores took just under two minutes(!) walltime
for the single Perl invocation to check all scripts in the project.

So, at this point, I have no hope for making linting fast on Windows;
it seems to be a lost cause.

> And if we did cache the results and avoid extra invocations via "make",
> then we'd want all the parallelism to move to there anyway.
>
> Maybe that gives you more food for thought about whether perl's "use
> threads" is worth having.

I'm not especially happy about the significant overhead of "ithreads";
on my (old) machine, although it does improve perceived time
significantly, it eats up quite a bit of additional user-time. As
such, I would not be unhappy to see "ithreads" go away, especially
since fast linting on Windows seems unattainable (at least with Perl).

Overall, I think Ævar's plan to parallelize linting via "make" is
probably the way to go.

  reply	other threads:[~2022-11-21  4:03 UTC|newest]

Thread overview: 51+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2022-09-01  0:29 [PATCH 00/18] make test "linting" more comprehensive Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 01/18] t: add skeleton chainlint.pl Eric Sunshine via GitGitGadget
2022-09-01 12:27   ` Ævar Arnfjörð Bjarmason
2022-09-02 18:53     ` Eric Sunshine
2022-09-01  0:29 ` [PATCH 02/18] chainlint.pl: add POSIX shell lexical analyzer Eric Sunshine via GitGitGadget
2022-09-01 12:32   ` Ævar Arnfjörð Bjarmason
2022-09-03  6:00     ` Eric Sunshine
2022-09-01  0:29 ` [PATCH 03/18] chainlint.pl: add POSIX shell parser Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 04/18] chainlint.pl: add parser to validate tests Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 05/18] chainlint.pl: add parser to identify test definitions Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 06/18] chainlint.pl: validate test scripts in parallel Eric Sunshine via GitGitGadget
2022-09-01 12:36   ` Ævar Arnfjörð Bjarmason
2022-09-03  7:51     ` Eric Sunshine
2022-09-06 22:35   ` Eric Wong
2022-09-06 22:52     ` Eric Sunshine
2022-09-06 23:26       ` Jeff King
2022-11-21  4:02         ` Eric Sunshine [this message]
2022-11-21 13:28           ` Ævar Arnfjörð Bjarmason
2022-11-21 14:07             ` Eric Sunshine
2022-11-21 14:18               ` Ævar Arnfjörð Bjarmason
2022-11-21 14:48                 ` Eric Sunshine
2022-11-21 18:04           ` Jeff King
2022-11-21 18:47             ` Eric Sunshine
2022-11-21 18:50               ` Eric Sunshine
2022-11-21 18:52               ` Jeff King
2022-11-21 19:00                 ` Eric Sunshine
2022-11-21 19:28                   ` Jeff King
2022-11-22  0:11                   ` Ævar Arnfjörð Bjarmason
2022-09-01  0:29 ` [PATCH 07/18] chainlint.pl: don't require `return|exit|continue` to end with `&&` Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 08/18] t/Makefile: apply chainlint.pl to existing self-tests Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 09/18] chainlint.pl: don't require `&` background command to end with `&&` Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 10/18] chainlint.pl: don't flag broken &&-chain if `$?` handled explicitly Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 11/18] chainlint.pl: don't flag broken &&-chain if failure indicated explicitly Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 12/18] chainlint.pl: complain about loops lacking explicit failure handling Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 13/18] chainlint.pl: allow `|| echo` to signal failure upstream of a pipe Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 14/18] t/chainlint: add more chainlint.pl self-tests Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 15/18] test-lib: retire "lint harder" optimization hack Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 16/18] test-lib: replace chainlint.sed with chainlint.pl Eric Sunshine via GitGitGadget
2022-09-03  5:07   ` Elijah Newren
2022-09-03  5:24     ` Eric Sunshine
2022-09-01  0:29 ` [PATCH 17/18] t/Makefile: teach `make test` and `make prove` to run chainlint.pl Eric Sunshine via GitGitGadget
2022-09-01  0:29 ` [PATCH 18/18] t: retire unused chainlint.sed Eric Sunshine via GitGitGadget
2022-09-02 12:42   ` several messages Johannes Schindelin
2022-09-02 18:16     ` Eric Sunshine
2022-09-02 18:34       ` Jeff King
2022-09-02 18:44         ` Junio C Hamano
2022-09-11  5:28 ` [PATCH 00/18] make test "linting" more comprehensive Jeff King
2022-09-11  7:01   ` Eric Sunshine
2022-09-11 18:31     ` Jeff King
2022-09-12 23:17       ` Eric Sunshine
2022-09-13  0:04         ` Jeff King

Reply instructions:

You may reply publicly to this message via plain-text email
using any one of the following methods:

* Save the following mbox file, import it into your mail client,
  and reply-to-all from there: mbox

  Avoid top-posting and favor interleaved quoting:
  https://en.wikipedia.org/wiki/Posting_style#Interleaved_style

* Reply using the --to, --cc, and --in-reply-to
  switches of git-send-email(1):

  git send-email \
    --in-reply-to=CAPig+cTge7kp9bH+Xd8wpqmEZuuEFE0xQdgqaFP1WAQ-F+xyHA@mail.gmail.com \
    --to=sunshine@sunshineco.com \
    --cc=Johannes.Schindelin@gmx.de \
    --cc=avarab@gmail.com \
    --cc=e@80x24.org \
    --cc=fs@gigacodes.de \
    --cc=git@vger.kernel.org \
    --cc=gitgitgadget@gmail.com \
    --cc=newren@gmail.com \
    --cc=peff@peff.net \
    /path/to/YOUR_REPLY

  https://kernel.org/pub/software/scm/git/docs/git-send-email.html

* If your mail client supports setting the In-Reply-To header
  via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).