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Date:   Tue, 12 Dec 2023 12:10:23 +0000
From:   Qais Yousef <qyousef@layalina.io>
To:     Lukasz Luba <lukasz.luba@arm.com>
Cc:     linux-kernel@vger.kernel.org,
        Vincent Guittot <vincent.guittot@linaro.org>,
        Viresh Kumar <viresh.kumar@linaro.org>,
        "Rafael J. Wysocki" <rafael@kernel.org>,
        Dietmar Eggemann <dietmar.eggemann@arm.com>,
        linux-pm@vger.kernel.org, Ingo Molnar <mingo@kernel.org>,
        Wei Wang <wvw@google.com>, Rick Yiu <rickyiu@google.com>,
        Chung-Kai Mei <chungkai@google.com>,
        Hongyan Xia <hongyan.xia2@arm.com>,
        Peter Zijlstra <peterz@infradead.org>
Subject: Re: [PATCH 1/4] sched/fair: Be less aggressive in calling
 cpufreq_update_util()
Message-ID: <20231212121023.mehtligcuwcmjtz4@airbuntu>
References: <20231208015242.385103-1-qyousef@layalina.io>
 <20231208015242.385103-2-qyousef@layalina.io>
 <bc525124-da79-45af-a99b-ec4616b3fa6b@arm.com>
 <20231210205156.kausxdcwsydggwie@airbuntu>
 <8ee6425a-0a0e-4391-9fd3-8fe74c809772@arm.com>
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On 12/11/23 07:56, Lukasz Luba wrote:
> 
> 
> On 12/10/23 20:51, Qais Yousef wrote:
> > On 12/08/23 10:05, Lukasz Luba wrote:
> > > Hi Qais,
> > > 
> > > On 12/8/23 01:52, Qais Yousef wrote:
> > > 
> > > [snip]
> > > 
> > > > @@ -6704,14 +6677,6 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
> > > >    	 */
> > > >    	util_est_enqueue(&rq->cfs, p);
> > > > -	/*
> > > > -	 * If in_iowait is set, the code below may not trigger any cpufreq
> > > > -	 * utilization updates, so do it here explicitly with the IOWAIT flag
> > > > -	 * passed.
> > > > -	 */
> > > > -	if (p->in_iowait)
> > > > -		cpufreq_update_util(rq, SCHED_CPUFREQ_IOWAIT);
> > > > -
> > > 
> > > Why this io wait boost is considered as the $subject says 'aggressive'
> > > calling?
> > 
> > This will trigger a frequency update along with the iowait boost. Did I miss
> > something?
> 
> Yes, it will change CPU freq and it was the main goal for this code
> path. We have tests which check how that works on different memory
> types.
> 
> Why do you want to remove it?

It seems you missed this hunk? I of course didn't remove it altogether if
that's what you mean :)

	@@ -6772,6 +6737,8 @@ enqueue_task_fair(struct rq *rq, struct task_struct *p, int flags)
	 enqueue_throttle:
		assert_list_leaf_cfs_rq(rq);

	+       cpufreq_update_util(rq, p->in_iowait ? SCHED_CPUFREQ_IOWAIT : 0);
	+
		hrtick_update(rq);
	 }

> 
> Did you run some tests (e.g. fio, gallery, etc) to check if you still
> have a decent performance out some new ufs/nvme memories?

PCMark storage gives

before*: 29681
after: 30014

* no patches applied including remove-margins one


Cheers

--
Qais Yousef

> 
> Beata & Dietmar have presented at LPC2021 a proposal to have a per-task
> io boost, with a bit more controllable way of the trade off power vs.
> performance [1]. IMO the io wait boost could evolve, not simply die.
> 
> Regards,
> Lukasz
> 
> [1] https://lpc.events/event/11/contributions/1042/