linux-kernel - Re: [External] Re: [PATCH 1/2] sched/fair: Fix cfs_rq_clock_pelt() for throttled cfs

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Date:   Fri, 8 Apr 2022 14:23:00 +0800
From:   Chengming Zhou <zhouchengming@...edance.com>
To:     Benjamin Segall <bsegall@...gle.com>
Cc:     mingo@...hat.com, peterz@...radead.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, mgorman@...e.de, bristot@...hat.com,
        linux-kernel@...r.kernel.org, duanxiongchun@...edance.com,
        songmuchun@...edance.com
Subject: Re: [External] Re: [PATCH 1/2] sched/fair: Fix cfs_rq_clock_pelt()
 for throttled cfs_rq

On 2022/4/8 04:57, Benjamin Segall wrote:
> Chengming Zhou <zhouchengming@...edance.com> writes:
> 
>> Since commit 23127296889f ("sched/fair: Update scale invariance of PELT")
>> change to use rq_clock_pelt() instead of rq_clock_task(), we should also
>> use rq_clock_pelt() for throttled_clock_task_time and throttled_clock_task
>> accounting.
> 
> I think this patch is indeed what we want, despite the confusing
> interactions between pelt slowdown+skipping and throttle_clock_task
> trying to freeze time.
> 
> I think it would be slightly better to rename
> throttled_clock_task(_time) to be clock_pelt rather than clock_task, but
> that's minor.

It's a good suggestion, will do and send v2.

Thanks.

> 
> Reviewed-by: Ben Segall <bsegall@...gle.com>
> 
>>
>> Fixes: 23127296889f ("sched/fair: Update scale invariance of PELT")
>> Signed-off-by: Chengming Zhou <zhouchengming@...edance.com>
>> ---
>>  kernel/sched/fair.c | 6 +++---
>>  1 file changed, 3 insertions(+), 3 deletions(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index d4bd299d67ab..e6fa5d1141b4 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -4846,7 +4846,7 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
>>  
>>  	cfs_rq->throttle_count--;
>>  	if (!cfs_rq->throttle_count) {
>> -		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
>> +		cfs_rq->throttled_clock_task_time += rq_clock_pelt(rq) -
>>  					     cfs_rq->throttled_clock_task;
>>  
>>  		/* Add cfs_rq with load or one or more already running entities to the list */
>> @@ -4864,7 +4864,7 @@ static int tg_throttle_down(struct task_group *tg, void *data)
>>  
>>  	/* group is entering throttled state, stop time */
>>  	if (!cfs_rq->throttle_count) {
>> -		cfs_rq->throttled_clock_task = rq_clock_task(rq);
>> +		cfs_rq->throttled_clock_task = rq_clock_pelt(rq);
>>  		list_del_leaf_cfs_rq(cfs_rq);
>>  	}
>>  	cfs_rq->throttle_count++;
>> @@ -5308,7 +5308,7 @@ static void sync_throttle(struct task_group *tg, int cpu)
>>  	pcfs_rq = tg->parent->cfs_rq[cpu];
>>  
>>  	cfs_rq->throttle_count = pcfs_rq->throttle_count;
>> -	cfs_rq->throttled_clock_task = rq_clock_task(cpu_rq(cpu));
>> +	cfs_rq->throttled_clock_task = rq_clock_pelt(cpu_rq(cpu));
>>  }
>>  
>>  /* conditionally throttle active cfs_rq's from put_prev_entity() */