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SubjectRe: [PATCH] sched/fair: Optimize select_idle_cpu
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On 2019/12/12 23:44, Valentin Schneider wrote:
> On 12/12/2019 15:24, Peter Zijlstra wrote:
>> On Thu, Dec 12, 2019 at 10:41:02PM +0800, Cheng Jian wrote:
>>
>>> Fixes: 1ad3aaf3fcd2 ("sched/core: Implement new approach to scale select_idle_cpu()")
>> The 'funny' thing is that select_idle_core() actually does the right
>> thing.
>>
>> Copying that should work:
>>
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 08a233e97a01..416d574dcebf 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -5828,6 +5837,7 @@ static inline int select_idle_smt(struct task_struct *p, int target)
>> */
>> static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int target)
>> {
>> + struct cpumask *cpus = this_cpu_cpumask_var_ptr(select_idle_mask);
>> struct sched_domain *this_sd;
>> u64 avg_cost, avg_idle;
>> u64 time, cost;
>> @@ -5859,11 +5869,11 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
>>
>> time = cpu_clock(this);
>>
>> - for_each_cpu_wrap(cpu, sched_domain_span(sd), target) {
>> + cpumask_and(cpus, sched_domain_span(sd), p->cpus_ptr);
>> +
>> + for_each_cpu_wrap(cpu, cpus, target) {
>> if (!--nr)
>> return si_cpu;
>> - if (!cpumask_test_cpu(cpu, p->cpus_ptr))
>> - continue;
>> if (available_idle_cpu(cpu))
>> break;
>> if (si_cpu == -1 && sched_idle_cpu(cpu))
>>
> That looks sane enough. I'd only argue the changelog should directly point
> out that the issue is we consume some CPUs out of 'nr' that are not allowed
> for the task and thus waste our attempts.
>
> .


Hi,Valentin

Yeah,Yours are more clear.

Thank you so much.


-- Cheng Jian



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