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From:   Jonathan Corbet <corbet@lwn.net>
To:     Feng Tang <feng.tang@intel.com>, linux-doc@vger.kernel.org,
        linux-kernel@vger.kernel.org, Randy Dunlap <rdunlap@infradead.org>,
        Bagas Sanjaya <bagasdotme@gmail.com>,
        Shakeel Butt <shakeelb@google.com>,
        Tim Chen <tim.c.chen@linux.intel.com>
Cc:     Arnaldo Carvalho de Melo <acme@redhat.com>,
        Joe Mario <jmario@redhat.com>, Ingo Molnar <mingo@redhat.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Andrew Morton <akpm@linux-foundation.org>,
        Eric Dumazet <edumazet@google.com>,
        Thomas Gleixner <tglx@linutronix.de>, dave.hansen@intel.com,
        ying.huang@intel.com, andi.kleen@intel.com,
        Feng Tang <feng.tang@intel.com>
Subject: Re: [PATCH v4] Documentation: Add document for false sharing
In-Reply-To: <20230407041235.37886-1-feng.tang@intel.com>
References: <20230407041235.37886-1-feng.tang@intel.com>
Date:   Mon, 10 Apr 2023 16:38:19 -0600
Message-ID: <877cuje52c.fsf@meer.lwn.net>
MIME-Version: 1.0
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Feng Tang <feng.tang@intel.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@intel.com>
> Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
> Reviewed-by: Shakeel Butt <shakeelb@google.com>

Applied, thanks.

jon