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

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Message-ID: <20210728204720.GN4397@paulmck-ThinkPad-P17-Gen-1>
Date:   Wed, 28 Jul 2021 13:47:20 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Josh Triplett <josh@...htriplett.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 01:37:19PM -0700, Josh Triplett wrote:
> 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?

None that I know of!

							Thanx, Paul