linux-kernel - Re: [PATCH rcu 06/11] osnoise: provide quiescent states

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Message-ID: <hrwgh7fevnkmkaizc7226kyywgzi22efmtnepzwah7ticrozbv@lcg23v6j7p7g>
Date: Tue, 4 Mar 2025 18:54:38 -0800
From: Boqun Feng <boqun.feng@...il.com>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: rcu@...r.kernel.org, "Paul E. McKenney" <paulmck@...nel.org>,
 	Frederic Weisbecker <frederic@...nel.org>,
 Neeraj Upadhyay <neeraj.upadhyay@...nel.org>,
 	Joel Fernandes <joel@...lfernandes.org>,
 Josh Triplett <josh@...htriplett.org>,
 	Uladzislau Rezki <urezki@...il.com>,
 Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
 	Lai Jiangshan <jiangshanlai@...il.com>,
 Zqiang <qiang.zhang1211@...il.com>, 	Davidlohr Bueso <dave@...olabs.net>,
 Ingo Molnar <mingo@...hat.com>, 	Peter Zijlstra <peterz@...radead.org>,
 Juri Lelli <juri.lelli@...hat.com>,
 	Vincent Guittot <vincent.guittot@...aro.org>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
 	Valentin Schneider <vschneid@...hat.com>,
 Masami Hiramatsu <mhiramat@...nel.org>, 	Shuah Khan <shuah@...nel.org>,
 Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
 	Clark Williams <clrkwllms@...nel.org>, linux-kernel@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, 	linux-kselftest@...r.kernel.org,
 linux-rt-devel@...ts.linux.dev, 	Ankur Arora <ankur.a.arora@...cle.com>
Subject: Re: [PATCH rcu 06/11] osnoise: provide quiescent states

On Tue, Mar 04, 2025 at 02:21:27PM -0500, Steven Rostedt wrote:
> On Mon, 24 Feb 2025 19:55:11 -0800
> Boqun Feng <boqun.feng@...il.com> wrote:
> 
> > From: Ankur Arora <ankur.a.arora@...cle.com>
> > 
> > To reduce RCU noise for nohz_full configurations, osnoise depends
> > on cond_resched() providing quiescent states for PREEMPT_RCU=n
> > configurations. For PREEMPT_RCU=y configurations -- where
> > cond_resched() is a stub -- we do this by directly calling
> > rcu_momentary_eqs().
> > 
> > With (PREEMPT_LAZY=y, PREEMPT_DYNAMIC=n), however, we have a
> > configuration with (PREEMPTION=y, PREEMPT_RCU=n) where neither
> > of the above can help.
> > 
> > Handle that by providing an explicit quiescent state here for all
> > configurations.
> > 
> > As mentioned above this is not needed for non-stubbed cond_resched(),
> > but, providing a quiescent state here just pulls in one that a future
> > cond_resched() would provide, so doesn't cause any extra work for
> > this configuration.
> > 
> > Cc: Paul E. McKenney <paulmck@...nel.org>
> > Cc: Daniel Bristot de Oliveira <bristot@...nel.org>
> > Cc: Steven Rostedt <rostedt@...dmis.org>
> 
> Acked-by: Steven Rostedt (Google) <rostedt@...dmis.org>
> 

Applied, thanks!

Regards,
Boqun

> -- Steve
> 
> > Suggested-by: Paul E. McKenney <paulmck@...nel.org>
> > Acked-by: Daniel Bristot de Oliveira <bristot@...nel.org>
> > Signed-off-by: Ankur Arora <ankur.a.arora@...cle.com>
> > Reviewed-by: Frederic Weisbecker <frederic@...nel.org>
> > Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
> > Signed-off-by: Boqun Feng <boqun.feng@...il.com>
> > ---