linux-kernel - Re: [PATCH] sched/fair: avoid !CONFIG_SMP cpufreq update callbacks when go idle

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Message-ID: <20160627083721.GY30154@twins.programming.kicks-ass.net>
Date:	Mon, 27 Jun 2016 10:37:21 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	mingo@...hat.com, rafael.j.wysocki@...el.com,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sched/fair: avoid !CONFIG_SMP cpufreq update callbacks
 when go idle

On Mon, Jun 27, 2016 at 03:56:03PM +0800, Jisheng Zhang wrote:
> This is to avoid cpufreq update callbacks when we go idle on UP
> platforms.

How so? the patch only avoids calling the update for (!root) cgroups --
which makes sense, but I'm not seeing how that's related to going idle,
or UP at all.

> 
> Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> ---
>  kernel/sched/fair.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index bdcbeea..236ec5b 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -3121,7 +3121,8 @@ static inline void update_load_avg(struct sched_entity *se, int not_used)
>  	struct cfs_rq *cfs_rq = cfs_rq_of(se);
>  	struct rq *rq = rq_of(cfs_rq);
>  
> -	cpufreq_trigger_update(rq_clock(rq));
> +	if (&rq->cfs == cfs_rq)
> +		cpufreq_trigger_update(rq_clock(rq));
>  }
>  
>  static inline void
> -- 
> 2.8.1
>