linux-kernel - Re: [PATCH] psi: Only collect online cpu time in collect_percpu

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Message-ID: <20191204123500.GT2844@hirez.programming.kicks-ass.net>
Date:   Wed, 4 Dec 2019 13:35:00 +0100
From:   Peter Zijlstra <peterz@...radead.org>
To:     Liu Song <fishland@...yun.com>
Cc:     mingo@...hat.com, linux-kernel@...r.kernel.org,
        liu.song11@....com.cn
Subject: Re: [PATCH] psi: Only collect online cpu time in collect_percpu_times

On Mon, Dec 02, 2019 at 09:09:28PM +0800, Liu Song wrote:
> From: Liu Song <liu.song11@....com.cn>
> 
> Tasks can only run on the online cpu, so only need to
> collect the time of the online cpu.
> 
> Signed-off-by: Liu Song <liu.song11@....com.cn>
> ---
>  kernel/sched/psi.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/psi.c b/kernel/sched/psi.c
> index 7acc632c3b82..605f02facb7b 100644
> --- a/kernel/sched/psi.c
> +++ b/kernel/sched/psi.c
> @@ -316,7 +316,7 @@ static void collect_percpu_times(struct psi_group *group,
>  	 * the sampling period. This eliminates artifacts from uneven
>  	 * loading, or even entirely idle CPUs.
>  	 */
> -	for_each_possible_cpu(cpu) {
> +	for_each_online_cpu(cpu) {
>  		u32 times[NR_PSI_STATES];
>  		u32 nonidle;
>  		u32 cpu_changed_states;

And who collects the deltas that remain after offline?