linux-kernel - Re: [PATCH 1/4] sched/fair: Be less aggressive in calling cpufreq_update

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Date:   Thu, 14 Dec 2023 08:19:15 +0000
From:   Lukasz Luba <lukasz.luba@....com>
To:     Qais Yousef <qyousef@...alina.io>
Cc:     linux-kernel@...r.kernel.org,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Viresh Kumar <viresh.kumar@...aro.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        linux-pm@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Wei Wang <wvw@...gle.com>, Rick Yiu <rickyiu@...gle.com>,
        Chung-Kai Mei <chungkai@...gle.com>,
        Hongyan Xia <hongyan.xia2@....com>,
        Peter Zijlstra <peterz@...radead.org>
Subject: Re: [PATCH 1/4] sched/fair: Be less aggressive in calling
 cpufreq_update_util()



On 12/12/23 12:10, Qais Yousef wrote:
> 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);
> 	 }
> 

Yes, you're right, I missed that change. I will have to spend some time
to figure out this new flow in the whole patch set.


>>
>> 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

The result looks good.

Thanks,
Lukasz