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

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Message-ID: <20250304142127.391ca6bd@gandalf.local.home>
Date: Tue, 4 Mar 2025 14:21:27 -0500
From: Steven Rostedt <rostedt@...dmis.org>
To: Boqun Feng <boqun.feng@...il.com>
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 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>

-- 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>
> ---