linux-kernel - Re: [RFCv5 PATCH 45/46] sched/cpufreq_sched: modify pcpu

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Date:	Sun, 16 Aug 2015 22:35:12 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Morten Rasmussen <morten.rasmussen@....com>
Cc:	mingo@...hat.com, vincent.guittot@...aro.org,
	daniel.lezcano@...aro.org,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	yuyang.du@...el.com, mturquette@...libre.com, rjw@...ysocki.net,
	Juri Lelli <Juri.Lelli@....com>, sgurrappadi@...dia.com,
	pang.xunlei@....com.cn, linux-kernel@...r.kernel.org,
	linux-pm@...r.kernel.org
Subject: Re: [RFCv5 PATCH 45/46] sched/cpufreq_sched: modify pcpu_capacity
 handling

On Tue, Jul 07, 2015 at 07:24:28PM +0100, Morten Rasmussen wrote:
> From: Juri Lelli <juri.lelli@....com>
> 
> Use the cpu argument of cpufreq_sched_set_cap() to handle per_cpu writes,
> as the thing can be called remotely (e.g., from load balacing code).
> 
> cc: Ingo Molnar <mingo@...hat.com>
> cc: Peter Zijlstra <peterz@...radead.org>
> 
> Signed-off-by: Juri Lelli <juri.lelli@....com>
> ---
>  kernel/sched/cpufreq_sched.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/sched/cpufreq_sched.c b/kernel/sched/cpufreq_sched.c
> index 06ff183..b81ac779 100644
> --- a/kernel/sched/cpufreq_sched.c
> +++ b/kernel/sched/cpufreq_sched.c
> @@ -151,7 +151,7 @@ void cpufreq_sched_set_cap(int cpu, unsigned long capacity)
>  	unsigned long capacity_max = 0;
>  
>  	/* update per-cpu capacity request */
> -	__this_cpu_write(pcpu_capacity, capacity);
> +	per_cpu(pcpu_capacity, cpu) = capacity;
>  
>  	policy = cpufreq_cpu_get(cpu);
>  	if (IS_ERR_OR_NULL(policy)) {

Uhm,.. this function seems to hard assume its called for the local CPU.
It will only use the irq_queue_work_on() if the cpufreq thing requires
the thread, otherwise it will call the method directly on the calling
cpu.
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