linux-kernel - Re: [PATCH v2 rcu 04/18] rcu: Weaken ->dynticks accesses and updates

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Date:   Wed, 28 Jul 2021 13:37:19 -0700
From:   Josh Triplett <josh@...htriplett.org>
To:     "Paul E. McKenney" <paulmck@...nel.org>
Cc:     rcu@...r.kernel.org, linux-kernel@...r.kernel.org,
        kernel-team@...com, mingo@...nel.org, jiangshanlai@...il.com,
        akpm@...ux-foundation.org, mathieu.desnoyers@...icios.com,
        tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
        dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
        oleg@...hat.com, joel@...lfernandes.org,
        Linus Torvalds <torvalds@...ux-foundation.org>
Subject: Re: [PATCH v2 rcu 04/18] rcu: Weaken ->dynticks accesses and updates

On Wed, Jul 28, 2021 at 10:37:15AM -0700, Paul E. McKenney wrote:
> This change makes the memory ordering requirements
> more evident, and it might well also speed up the to-idle and from-idle
> fastpaths on some architectures.

Cleaning up the memory ordering requirements certainly seems worthwhile.
But is there any straightforward benchmark that might quantify the
"might well also speed up" here? How much does weakening the memory
ordering buy us, in practice?