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From: Valentin Schneider <valentin.schneider@arm.com>
To: paulmck@kernel.org
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: Wed, 04 Aug 2021 11:18:11 +0100	[thread overview]
Message-ID: <87tuk5a4yk.mognet@arm.com> (raw)
In-Reply-To: <20210803234231.GW4397@paulmck-ThinkPad-P17-Gen-1>

On 03/08/21 16:42, Paul E. McKenney wrote:
> On Tue, Aug 03, 2021 at 11:54:37PM +0100, Valentin Schneider wrote:
>> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
>> index 680f66b65f14..3dd5fa75f469 100644
>> --- a/kernel/rcu/rcutorture.c
>> +++ b/kernel/rcu/rcutorture.c
>> @@ -948,12 +948,26 @@ static int rcu_torture_boost(void *arg)
>>      unsigned long endtime;
>>      unsigned long oldstarttime;
>>      struct rcu_boost_inflight rbi = { .inflight = 0 };
>> +	struct task_struct *ksoftirqd = this_cpu_ksoftirqd();
>>
>>      VERBOSE_TOROUT_STRING("rcu_torture_boost started");
>>
>>      /* Set real-time priority. */
>>      sched_set_fifo_low(current);
>>
>> +	/*
>> +	 * Boost testing requires TIMER_SOFTIRQ to run at a higher priority
>> +	 * than the CPU-hogging torture kthreads, otherwise said threads
>> +	 * will never let timer expiry for the RCU GP kthread happen, which will
>> +	 * prevent any boosting.
>> +	 */
>> +	if (current->normal_prio < ksoftirqd->normal_prio) {
>
> Would it make sense to add IS_ENABLED(CONFIG_PREEMPT_RT) to the above
> condition?
>

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.

>                                                       Thanx, Paul
>
>> +		struct sched_param sp = { .sched_priority = 2 };
>> +
>> +		pr_alert("%s(): Adjusting %s priority\n", __func__, ksoftirqd->comm);
>> +		sched_setscheduler_nocheck(ksoftirqd, SCHED_FIFO, &sp);
>> +	}
>> +
>>      init_rcu_head_on_stack(&rbi.rcu);
>>      /* Each pass through the following loop does one boost-test cycle. */
>>      do {
>> --
>> 2.25.1
>>

  reply	other threads:[~2021-08-04 10:18 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 [this message]
2021-08-04 22:53       ` Paul E. McKenney
2021-08-05 11:51         ` Valentin Schneider
2021-08-05 16:10           ` Paul E. McKenney

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