From: "Paul E. McKenney" <paulmck@kernel.org>
To: Valentin Schneider <valentin.schneider@arm.com>
Cc: linux-kernel@vger.kernel.org, rcu@vger.kernel.org,
linux-rt-users@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Thomas Gleixner <tglx@linutronix.de>,
Steven Rostedt <rostedt@goodmis.org>,
Daniel Bristot de Oliveira <bristot@redhat.com>,
Frederic Weisbecker <frederic@kernel.org>,
Josh Triplett <josh@joshtriplett.org>,
Davidlohr Bueso <dave@stgolabs.net>,
Mathieu Desnoyers <mathieu.desnoyers@efficios.com>,
Lai Jiangshan <jiangshanlai@gmail.com>,
Joel Fernandes <joel@joelfernandes.org>
Subject: Re: [PATCH 2/2] rcutorture: Nudge ksoftirqd priority for RCU boost testing
Date: Thu, 5 Aug 2021 09:10:49 -0700 [thread overview]
Message-ID: <20210805161049.GK4397@paulmck-ThinkPad-P17-Gen-1> (raw)
In-Reply-To: <87mtpw9kiz.mognet@arm.com>
On Thu, Aug 05, 2021 at 12:51:48PM +0100, Valentin Schneider wrote:
> On 04/08/21 15:53, Paul E. McKenney wrote:
> > On Wed, Aug 04, 2021 at 11:18:11AM +0100, Valentin Schneider wrote:
> >>
> >> Hm so v5.13-rt1 has this commit:
> >>
> >> 5e59fba573e6 ("rcutorture: Fix testing of RCU priority boosting")
> >>
> >> which gates RCU boost torture testing under CONFIG_PREEMPT_RT. Now, AFAICT
> >> the TIMER_SOFTIRQ priority problem is there regardless of
> >> CONFIG_PREEMPT_RT, so this patch would (should?) make sense even on
> >> !CONFIG_PREEMPT_RT.
> >
> > What rcutorture scenario TREE03 does is to boot with tree.use_softirq=0
> > and threadirqs. I see your point about timers and softirq, but this
> > does run reliably for me.
> >
> > Ah, I see why. Commit ea6d962e80b6 ("rcutorture: Judge RCU priority
> > boosting on grace periods, not callbacks") includes boosting the priority
> > of the ksoftirqd kthreads. But only when running rcutorture builtin,
> > not as a module. Here is the code in rcu_torture_init():
> >
> > // Testing RCU priority boosting requires rcutorture do
> > // some serious abuse. Counter this by running ksoftirqd
> > // at higher priority.
> > if (IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)) {
> > for_each_online_cpu(cpu) {
> > struct sched_param sp;
> > struct task_struct *t;
> >
> > t = per_cpu(ksoftirqd, cpu);
> > WARN_ON_ONCE(!t);
> > sp.sched_priority = 2;
> > sched_setscheduler_nocheck(t, SCHED_FIFO, &sp);
> > }
> > }
> >
> > I take it that you were running rcutorture as a module?
> >
> > This describes how to run it built-in, if that works for you:
> >
> > https://paulmck.livejournal.com/61432.html
> >
> > More specifically: https://paulmck.livejournal.com/57769.html
> >
> > Alternatively, the "IS_BUILTIN(CONFIG_RCU_TORTURE_TEST)" check could be
> > removed in the above code, and the ksoftirqd kthreads could have their
> > original priority restored in rcu_torture_cleanup().
> >
> > Thoughts?
>
> I actually run rcutorture as a builtin, but from what I can tell the above
> patch came in v5.14-rc1, and ofc I'm running my tests on v5.13-rt1... I
> should have paid closer attention to what was in the latest mainline,
> apologies for the noise.
Not a problem, and thank you for giving rcutorture a try!
> FWIW tweaking ksoftirqd priority only when the torture module is builtin
> makes sense to me.
Very good, I will stick with the status quo, then.
Thanx, Paul
prev parent reply other threads:[~2021-08-05 16:10 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-08-03 22:54 [PATCH 0/2] rcutorture: Some PREEMPT_RT fixlets Valentin Schneider
2021-08-03 22:54 ` [PATCH 1/2] rcutorture: Don't disable softirqs with preemption disabled when PREEMPT_RT Valentin Schneider
2021-08-03 23:43 ` Paul E. McKenney
2021-08-04 10:17 ` Valentin Schneider
2021-08-04 22:37 ` Paul E. McKenney
2021-08-03 22:54 ` [PATCH 2/2] rcutorture: Nudge ksoftirqd priority for RCU boost testing Valentin Schneider
2021-08-03 23:42 ` Paul E. McKenney
2021-08-04 10:18 ` Valentin Schneider
2021-08-04 22:53 ` Paul E. McKenney
2021-08-05 11:51 ` Valentin Schneider
2021-08-05 16:10 ` Paul E. McKenney [this message]
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