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Re: [RFCv5 PATCH 45/46] sched/cpufreq_sched: modify pcpu_capacity handling

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  Re: [RFCv5 PATCH 45/46] sched/cpufreq_sched: modify pcpu_capacity  handling Peter Zijlstra <peterz@infradead.org> - 2015-08-17 00:10 +0200
    Re: [RFCv5 PATCH 45/46] sched/cpufreq_sched: modify pcpu_capacity  handling Juri Lelli <juri.lelli@arm.com> - 2015-08-17 13:20 +0200

#1208279 — 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@arm.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@redhat.com>
> cc: Peter Zijlstra <peterz@infradead.org>
> 
> Signed-off-by: Juri Lelli <juri.lelli@arm.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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#1208534

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@arm.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@redhat.com>
>> cc: Peter Zijlstra <peterz@infradead.org>
>>
>> Signed-off-by: Juri Lelli <juri.lelli@arm.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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