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

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Date:	Mon, 17 Aug 2015 12:16:12 +0100
From:	Juri Lelli <juri.lelli@....com>
To:	Peter Zijlstra <peterz@...radead.org>,
	Morten Rasmussen <Morten.Rasmussen@....com>
CC:	"mingo@...hat.com" <mingo@...hat.com>,
	"vincent.guittot@...aro.org" <vincent.guittot@...aro.org>,
	"daniel.lezcano@...aro.org" <daniel.lezcano@...aro.org>,
	Dietmar Eggemann <Dietmar.Eggemann@....com>,
	"yuyang.du@...el.com" <yuyang.du@...el.com>,
	"mturquette@...libre.com" <mturquette@...libre.com>,
	"rjw@...ysocki.net" <rjw@...ysocki.net>,
	"sgurrappadi@...dia.com" <sgurrappadi@...dia.com>,
	"pang.xunlei@....com.cn" <pang.xunlei@....com.cn>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>
Subject: Re: [RFCv5 PATCH 45/46] sched/cpufreq_sched: modify pcpu_capacity
 handling

Hi Peter,

On 16/08/15 21:35, Peter Zijlstra wrote:
> 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.
> 

True, but we still retrieve policy from cpu passed as argument; and
then we use policy to request a freq transition, that should end up
updating the right cpu.

Thanks,

- Juri

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