linux-kernel - Re: [PATCH] af_unix: annotate unix_gc_lock with __cacheline_aligned_in

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Message-ID: <CAAVpQUAfDxZfbeM8nSYH611oTfagnpbvK4FQ5H83h3vTd9NGfw@mail.gmail.com>
Date: Mon, 8 Dec 2025 00:24:16 -0800
From: Kuniyuki Iwashima <kuniyu@...gle.com>
To: Mateusz Guzik <mjguzik@...il.com>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org, kuba@...nel.org, 
	oliver.sang@...el.com
Subject: Re: [PATCH] af_unix: annotate unix_gc_lock with __cacheline_aligned_in_smp

On Wed, Dec 3, 2025 at 2:01 AM Mateusz Guzik <mjguzik@...il.com> wrote:
>
> Otherwise the lock is susceptible to ever-changing false-sharing due to
> unrelated changes. This in particular popped up here where an unrelated
> change improved performance:
> https://lore.kernel.org/oe-lkp/202511281306.51105b46-lkp@intel.com/
>
> Stabilize it with an explicit annotation which also has a side effect
> of furher improving scalability:
> > in our oiginal report, 284922f4c5 has a 6.1% performance improvement comparing
> > to parent 17d85f33a8.
> > we applied your patch directly upon 284922f4c5. as below, now by
> > "284922f4c5 + your patch"
> > we observe a 12.8% performance improvements (still comparing to 17d85f33a8).
>
> Note nothing was done for the other fields, so some fluctuation is still
> possible.
>
> Tested-by: kernel test robot <oliver.sang@...el.com>
> Signed-off-by: Mateusz Guzik <mjguzik@...il.com>

Reviewed-by: Kuniyuki Iwashima <kuniyu@...gle.com>