linux-kernel - Re: [PATCH v2] sched: Consolidate cpufreq updates

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Date: Tue, 7 May 2024 10:02:30 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: Qais Yousef <qyousef@...alina.io>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>,
	Viresh Kumar <viresh.kumar@...aro.org>,
	Ingo Molnar <mingo@...nel.org>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Juri Lelli <juri.lelli@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Dietmar Eggemann <dietmar.eggemann@....com>,
	Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
	Daniel Bristot de Oliveira <bristot@...hat.com>,
	Valentin Schneider <vschneid@...hat.com>,
	Christian Loehle <christian.loehle@....com>,
	linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] sched: Consolidate cpufreq updates

On Tue, May 07, 2024 at 01:56:59AM +0100, Qais Yousef wrote:

> Yes. How about this? Since stopper class appears as RT, we should still check
> for this class specifically.

Much nicer!

> static inline void update_cpufreq_ctx_switch(struct rq *rq, struct task_struct *prev)
> {
> #ifdef CONFIG_CPU_FREQ
> 	if (likely(fair_policy(current->policy))) {
> 
> 		if (unlikely(current->in_iowait)) {
> 			cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT | SCHED_CPUFREQ_FORCE_UPDATE);
> 			return;
> 		}
> 
> #ifdef CONFIG_SMP
> 		/*
> 		 * Allow cpufreq updates once for every update_load_avg() decay.
> 		 */
> 		if (unlikely(rq->cfs.decayed)) {
> 			rq->cfs.decayed = false;
> 			cpufreq_update_util(rq, 0);
> 			return;
> 		}
> #endif
> 		return;
> 	}
> 
> 	/*
> 	 * RT and DL should always send a freq update. But we can do some
> 	 * simple checks to avoid it when we know it's not necessary.
> 	 */
> 	if (task_is_realtime(current)) {
> 		if (dl_task(current) && current->dl.flags & SCHED_FLAG_SUGOV) {
> 			/* Ignore sugov kthreads, they're responding to our requests */
> 			return;
> 		}
> 
> 		if (rt_task(current) && rt_task(prev)) {

doesn't task_is_realtime() impy rt_task() ?

Also, this clause still includes DL tasks, is that okay?

> #ifdef CONFIG_UCLAMP_TASK
> 			unsigned long curr_uclamp_min = uclamp_eff_value(current, UCLAMP_MIN);
> 			unsigned long prev_uclamp_min = uclamp_eff_value(prev, UCLAMP_MIN);
> 
> 			if (curr_uclamp_min == prev_uclamp_min)
> #endif
> 				return;
> 		}
> 
> #ifdef CONFIG_SMP
> 		if (unlikely(current->sched_class == &stop_sched_class))
> 			return;
> #endif
> 
> 		cpufreq_update_util(rq, SCHED_CPUFREQ_FORCE_UPDATE);
> 		return;
> 	}
> 
> 	/* Everything else shouldn't trigger a cpufreq update */
> 	return;
> #endif
> }