linux-kernel - Re: [PATCH v4 08/10] sched/fair: Steal work from an overloaded CPU when CPU goes idle

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Message-ID: <3d017a5d-50a4-3e99-c3c8-9b3ee240d076@arm.com>
Date:   Sat, 8 Dec 2018 18:39:21 +0000
From:   Valentin Schneider <valentin.schneider@....com>
To:     Steven Sistare <steven.sistare@...cle.com>, mingo@...hat.com,
        peterz@...radead.org
Cc:     subhra.mazumdar@...cle.com, dhaval.giani@...cle.com,
        daniel.m.jordan@...cle.com, pavel.tatashin@...rosoft.com,
        matt@...eblueprint.co.uk, umgwanakikbuti@...il.com,
        riel@...hat.com, jbacik@...com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, quentin.perret@....com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4 08/10] sched/fair: Steal work from an overloaded CPU
 when CPU goes idle

On 07/12/2018 22:36, Steven Sistare wrote:
> On 12/7/2018 3:21 PM, Valentin Schneider wrote:
>> Hi Steve,
>>
>> On 06/12/2018 21:28, Steve Sistare wrote:
>> [...]
>>> @@ -6778,20 +6791,22 @@ static void check_preempt_wakeup(struct rq *rq, struct task_struct *p, int wake_
>>>  	update_misfit_status(NULL, rq);
>>>  
>>>  	/*
>>> -	 * We must set idle_stamp _before_ calling idle_balance(), such that we
>>> -	 * measure the duration of idle_balance() as idle time.
>>> +	 * We must set idle_stamp _before_ calling try_steal() or
>>> +	 * idle_balance(), such that we measure the duration as idle time.
>>>  	 */
>>>  	rq_idle_stamp_update(rq); 
>>
>> idle_balance() has a
>>
>> 	/*
>> 	 * Do not pull tasks towards !active CPUs...
>> 	 */
>> 	if (!cpu_active(this_cpu))
>> 		return 0;
>>
>> check which we probably want for stealing too, so we could hoist it up here
>> to cover both idle_balance() and try_steal().
> 
> try_steal() already checks cpu_active.  I could hoist it.
> 

Ah yeah I missed that one, I had only seen cpu_active(src_cpu) in steal_from().
It's all good then.

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