linux-kernel - Re: [PATCH] sched: fix incorrect wait time and wait count statistics

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Date:	Mon, 26 Oct 2015 18:44:48 -0700
From:	Joonwoo Park <joonwoop@...eaurora.org>
To:	Peter Zijlstra <peterz@...radead.org>
CC:	Ingo Molnar <mingo@...nel.org>, linux-kernel@...r.kernel.org,
	linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH] sched: fix incorrect wait time and wait count statistics

On 10/25/2015 03:26 AM, Peter Zijlstra wrote:
> On Sat, Oct 24, 2015 at 10:23:14PM -0700, Joonwoo Park wrote:
>> @@ -1069,7 +1069,7 @@ static struct rq *move_queued_task(struct rq *rq, struct task_struct *p, int new
>>  {
>>  	lockdep_assert_held(&rq->lock);
>>  
>> -	dequeue_task(rq, p, 0);
>> +	dequeue_task(rq, p, DEQUEUE_MIGRATING);
>>  	p->on_rq = TASK_ON_RQ_MIGRATING;
>>  	set_task_cpu(p, new_cpu);
>>  	raw_spin_unlock(&rq->lock);
> 
>> @@ -5656,7 +5671,7 @@ static void detach_task(struct task_struct *p, struct lb_env *env)
>>  {
>>  	lockdep_assert_held(&env->src_rq->lock);
>>  
>> -	deactivate_task(env->src_rq, p, 0);
>> +	deactivate_task(env->src_rq, p, DEQUEUE_MIGRATING);
>>  	p->on_rq = TASK_ON_RQ_MIGRATING;
>>  	set_task_cpu(p, env->dst_cpu);
>>  }
> 
> Also note that on both sites we also set TASK_ON_RQ_MIGRATING -- albeit
> late. Can't you simply set that earlier (and back to QUEUED later) and
> test for task_on_rq_migrating() instead of blowing up the fastpath like
> you did?
> 

Yes it's doable.  I also find it's much simpler.
Please find patch v2.  I verified v2 does same job as v1 by comparing sched_stat_wait time with sched_switch - sched_wakeup timestamp.

Thanks,
Joonwoo

View attachment "0001-sched-fix-incorrect-wait-time-and-wait-count-statist.patch" of type "text/x-patch" (3925 bytes)