linux-kernel - Re: [PATCH v3] locking/rwsem: Add __always_inline annotation to __down_read

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Date:   Mon, 8 May 2023 10:23:56 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     John Stultz <jstultz@...gle.com>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Minchan Kim <minchan@...nel.org>,
        Tim Murray <timmurray@...gle.com>,
        Ingo Molnar <mingo@...hat.com>, Will Deacon <will@...nel.org>,
        Waiman Long <longman@...hat.com>,
        Boqun Feng <boqun.feng@...il.com>, kernel-team@...roid.com,
        stable@...r.kernel.org
Subject: Re: [PATCH v3] locking/rwsem: Add __always_inline annotation to
 __down_read_common() and inlined callers

On Wed, May 03, 2023 at 02:33:51AM +0000, John Stultz wrote:
> Apparently despite it being marked inline, the compiler
> may not inline __down_read_common() which makes it difficult
> to identify the cause of lock contention, as the blocked
> function in traceevents will always be listed as
> __down_read_common().
> 
> So this patch adds __always_inline annotation to the common
> function (as well as the inlined helper callers) to force it to
> be inlined so the blocking function will be listed (via Wchan)
> in traceevents.
> 
> Cc: Minchan Kim <minchan@...nel.org>
> Cc: Tim Murray <timmurray@...gle.com>
> Cc: Peter Zijlstra <peterz@...radead.org>
> Cc: Ingo Molnar <mingo@...hat.com>
> Cc: Will Deacon <will@...nel.org>
> Cc: Waiman Long <longman@...hat.com>
> Cc: Boqun Feng <boqun.feng@...il.com>
> Cc: kernel-team@...roid.com
> Cc: stable@...r.kernel.org
> Fixes: c995e638ccbb ("locking/rwsem: Fold __down_{read,write}*()")
> Reviewed-by: Waiman Long <longman@...hat.com>
> Reported-by: Tim Murray <timmurray@...gle.com>
> Signed-off-by: John Stultz <jstultz@...gle.com>

Thanks!