Re: [PATCH] sched/fair: Optimize select_idle_cpu

[chengjian (D)]

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.
>
> .


HiïValentin

YeahïYours are more clear.

Thank you so much.


-- Cheng Jian