linux-kernel - Re: [PATCH v4] Documentation: Add document for false sharing

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Message-ID: <877cuje52c.fsf@meer.lwn.net>
Date:   Mon, 10 Apr 2023 16:38:19 -0600
From:   Jonathan Corbet <corbet@....net>
To:     Feng Tang <feng.tang@...el.com>, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, Randy Dunlap <rdunlap@...radead.org>,
        Bagas Sanjaya <bagasdotme@...il.com>,
        Shakeel Butt <shakeelb@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@...hat.com>,
        Joe Mario <jmario@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Thomas Gleixner <tglx@...utronix.de>, dave.hansen@...el.com,
        ying.huang@...el.com, andi.kleen@...el.com,
        Feng Tang <feng.tang@...el.com>
Subject: Re: [PATCH v4] Documentation: Add document for false sharing

Feng Tang <feng.tang@...el.com> writes:

> When doing performance tuning or debugging performance regressions,
> more and more cases are found to be related to false sharing [1][2][3],
> and the situation can be worse for newer platforms with hundreds of
> CPUs. There are already many commits in current kernel specially
> for mitigating the performance degradation due to false sharing.
>
> False sharing could harm the performance silently without being
> noticed, due to reasons like:
> * data members of a big data structure randomly sitting together
>   in one cache line
> * global data of small size are linked compactly together
>
> So it's better to make a simple document about the normal pattern
> of false sharing, basic ways to mitigate it and call out to
> developers to pay attention during code-writing.
>
> [ Many thanks to Dave Hansen, Ying Huang, Tim Chen, Julie Du and
>   Yu Chen for their contributions ]
>
> [1]. https://lore.kernel.org/lkml/20220619150456.GB34471@xsang-OptiPlex-9020/
> [2]. https://lore.kernel.org/lkml/20201102091543.GM31092@shao2-debian/
> [3]. https://lore.kernel.org/lkml/20230307125538.818862491@linutronix.de/
>
> Signed-off-by: Feng Tang <feng.tang@...el.com>
> Reviewed-by: Randy Dunlap <rdunlap@...radead.org>
> Reviewed-by: Shakeel Butt <shakeelb@...gle.com>

Applied, thanks.

jon