linux-kernel - Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock

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Message-ID: <xm2637ppzsfz.fsf@bsegall-linux.mtv.corp.google.com>
Date:	Tue, 10 May 2016 11:19:44 -0700
From:	bsegall@...gle.com
To:	Xunlei Pang <xlpang@...hat.com>
Cc:	linux-kernel@...r.kernel.org,
	Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@....com>,
	Ingo Molnar <mingo@...hat.com>,
	Steven Rostedt <rostedt@...dmis.org>, pjt@...gle.com
Subject: Re: [PATCH] sched/fair: Fix the wrong throttled clock time for cfs_rq_clock_task()

Xunlei Pang <xlpang@...hat.com> writes:

> Two minor fixes for cfs_rq_clock_task().
> 1) If cfs_rq is currently being throttled, we need to subtract the cfs
>    throttled clock time.
>
> 2) Make "throttled_clock_task_time" update SMP unrelated. Now UP cases
>    need it as well.
>
> Signed-off-by: Xunlei Pang <xlpang@...hat.com>
> ---
>  kernel/sched/fair.c | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 1708729e..fb80a12 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3655,7 +3655,7 @@ static inline struct cfs_bandwidth *tg_cfs_bandwidth(struct task_group *tg)
>  static inline u64 cfs_rq_clock_task(struct cfs_rq *cfs_rq)
>  {
>  	if (unlikely(cfs_rq->throttle_count))
> -		return cfs_rq->throttled_clock_task;
> +		return cfs_rq->throttled_clock_task - cfs_rq->throttled_clock_task_time;
>  
>  	return rq_clock_task(rq_of(cfs_rq)) - cfs_rq->throttled_clock_task_time;
>  }
> @@ -3793,13 +3793,11 @@ static int tg_unthrottle_up(struct task_group *tg, void *data)
>  	struct cfs_rq *cfs_rq = tg->cfs_rq[cpu_of(rq)];
>  
>  	cfs_rq->throttle_count--;
> -#ifdef CONFIG_SMP
>  	if (!cfs_rq->throttle_count) {
>  		/* adjust cfs_rq_clock_task() */
>  		cfs_rq->throttled_clock_task_time += rq_clock_task(rq) -
>  					     cfs_rq->throttled_clock_task;
>  	}
> -#endif
>  
>  	return 0;
>  }

[Cc: pjt@...gle.com]

This looks reasonable to me (at least the first part; I'm not
certain why the CONFIG_SMP ifdef was put in place).