From: Thomas Rast <trast@inf•ethz.ch>
To: "Nguyễn Thái Ngọc Duy" <pclouds@gmail•com>
Cc: <git@vger•kernel.org>, Junio C Hamano <gitster@pobox•com>,
Ramsay Jones <ramsay@ramsay1•demon.co.uk>
Subject: Re: [PATCH v2 2/2] index-pack: support multithreaded delta resolving
Date: Mon, 12 Mar 2012 11:57:41 +0100 [thread overview]
Message-ID: <87y5r684t6.fsf@thomas.inf.ethz.ch> (raw)
In-Reply-To: <1331519549-28090-3-git-send-email-pclouds@gmail.com> ("Nguyễn Thái Ngọc Duy"'s message of "Mon, 12 Mar 2012 09:32:29 +0700")
Nguyễn Thái Ngọc Duy <pclouds@gmail•com> writes:
> This puts delta resolving on each base on a separate thread, one base
> cache per thread. Per-thread data is grouped in struct thread_local.
> When running with nr_threads == 1, no pthreads calls are made. The
> system essentially runs in non-thread mode.
As discussed when we took the git-grep measurements, it may be
interesting to have a way to run 1 thread. Can you put in such an
option?
> An experiment on a Xeon 24 core machine with linux-2.6.git shows that
> performance does not increase proportional to the number of cores. So
> by default, we use maximum 3 cores. Some numbers with --threads from 1
> to 16:
>
> 1..4
> real 1m16.310s 0m48.183s 0m37.866s 0m32.834s
> user 1m13.773s 1m15.537s 1m15.781s 1m16.233s
> sys 0m2.480s 0m3.936s 0m4.448s 0m4.852s
>
> 5..8
> real 0m33.170s 0m30.369s 0m28.406s 0m26.968s
> user 1m31.474s 1m30.322s 1m29.562s 1m28.694s
> sys 0m6.096s 0m6.268s 0m6.684s 0m7.172s
Interesting. Is this a real 24-core machine or 12*2 hyperthreaded?
Does it use Turbo Boost and how far (how fast and on how many cores
simultaneously) does that go?
I'm asking because if Turbo Boost starts to wear off around 4 cores,
like these measurements suggest, then it may not be beneficial to spawn
threads on 2*2HT CPUs (found in many laptops) where Turbo Boost only
really works if you only use a single core.
Oh, and could you write a perf test for this? :-)
--
Thomas Rast
trast@{inf,student}.ethz.ch
next prev parent reply other threads:[~2012-03-12 10:58 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-03-12 2:32 [PATCH v2 0/2] Multithread index-pack Nguyễn Thái Ngọc Duy
2012-03-12 2:32 ` [PATCH v2 1/2] index-pack: split second pass obj handling into own function Nguyễn Thái Ngọc Duy
2012-03-12 2:32 ` [PATCH v2 2/2] index-pack: support multithreaded delta resolving Nguyễn Thái Ngọc Duy
2012-03-12 10:57 ` Thomas Rast [this message]
2012-03-12 11:42 ` Nguyen Thai Ngoc Duy
2012-03-12 11:47 ` Thomas Rast
2012-03-12 12:18 ` Nguyen Thai Ngoc Duy
2012-03-13 0:32 ` Ramsay Jones
2012-03-14 10:29 ` Nguyen Thai Ngoc Duy
-- strict thread matches above, loose matches on Subject: below --
2012-03-02 6:09 [PATCH " Junio C Hamano
2012-03-02 13:42 ` [PATCH v2 " Nguyễn Thái Ngọc Duy
2012-03-02 18:53 ` Junio C Hamano
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