linux-kernel - Re: [PATCH v2] locking/rwsem: Add __always_inline annotation to __down_read

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Message-ID: <20230417111949.GJ83892@hirez.programming.kicks-ass.net>
Date:   Mon, 17 Apr 2023 13:19:49 +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 v2] locking/rwsem: Add __always_inline annotation to
 __down_read_common()

On Wed, Apr 12, 2023 at 03:59:05AM +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 will always be listed as __down_read_common().
> 
> So this patch adds __always_inline annotation to the
> function to force it to be inlines so the calling function
> will be listed.

I'm a wee bit confused; what are you looking at? Wchan? What is stopping
the compiler from now handing you
__down_read{,_interruptible,_killable}() instead? Is that fine?