linux-kernel - Re: [RFC PATCH v7 09/23] sched/fair: Fix forced idle sibling starvation corner case

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Message-ID: <ea484c79-8606-4817-909c-fe4fd5e085d6@linux.microsoft.com>
Date:   Fri, 28 Aug 2020 19:24:04 -0400
From:   Vineeth Pillai <viremana@...ux.microsoft.com>
To:     Peter Zijlstra <peterz@...radead.org>,
        Julien Desfossez <jdesfossez@...italocean.com>
Cc:     Joel Fernandes <joelaf@...gle.com>,
        Tim Chen <tim.c.chen@...ux.intel.com>,
        Aaron Lu <aaron.lwe@...il.com>,
        Aubrey Li <aubrey.intel@...il.com>,
        Dhaval Giani <dhaval.giani@...cle.com>,
        Chris Hyser <chris.hyser@...cle.com>,
        Nishanth Aravamudan <naravamudan@...italocean.com>,
        mingo@...nel.org, tglx@...utronix.de, pjt@...gle.com,
        torvalds@...ux-foundation.org, linux-kernel@...r.kernel.org,
        fweisbec@...il.com, keescook@...omium.org, kerrnel@...gle.com,
        Phil Auld <pauld@...hat.com>,
        Valentin Schneider <valentin.schneider@....com>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@...ux.intel.com>,
        Paolo Bonzini <pbonzini@...hat.com>, joel@...lfernandes.org,
        vineeth@...byteword.org, Chen Yu <yu.c.chen@...el.com>,
        Christian Brauner <christian.brauner@...ntu.com>,
        Agata Gruza <agata.gruza@...el.com>,
        Antonio Gomez Iglesias <antonio.gomez.iglesias@...el.com>,
        graf@...zon.com, konrad.wilk@...cle.com, dfaggioli@...e.com,
        rostedt@...dmis.org, derkling@...gle.com, benbjiang@...cent.com
Subject: Re: [RFC PATCH v7 09/23] sched/fair: Fix forced idle sibling
 starvation corner case



On 8/28/20 5:25 PM, Peter Zijlstra wrote:
> The only pupose of this loop seem to be to find if we have a forceidle;
> surely we can avoid that by storing this during the pick.
The idea was to kick each cpu that was force idle. But now, thinking
about it, we just need to kick one as it will pick for all the siblings.
Will optimize this as you suggested.

>
> static void task_tick_core(struct rq *rq)
> {
> 	if (sched_core_enabled(rq))
> 		resched_forceidle_sibling(rq, &rq->curr->se);
> }
>
> #else
>
> static void task_tick_core(struct rq *rq) { }
>
>> +#endif
>> +
>>   /*
>>    * scheduler tick hitting a task of our scheduling class.
>>    *
>> @@ -10654,6 +10688,11 @@ static void task_tick_fair(struct rq *rq, struct task_struct *curr, int queued)
>>   
>>   	update_misfit_status(curr, rq);
>>   	update_overutilized_status(task_rq(curr));
>> +
>> +#ifdef CONFIG_SCHED_CORE
>> +	if (sched_core_enabled(rq))
>> +		resched_forceidle_sibling(rq, &curr->se);
>> +#endif
> Then you can ditch the #ifdef here
Makes sense, will do.

Thanks,
Vineeth