Re: [PATCH] sched/fair: Optimize select_idle_cpu

[chengjian (D)]

On 2019/12/12 23:04, Peter Zijlstra wrote:
> On Thu, Dec 12, 2019 at 10:41:02PM +0800, Cheng Jian wrote:
> > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> > index 08a233e97a01..16a29b570803 100644
> > --- a/kernel/sched/fair.c
> > +++ b/kernel/sched/fair.c
> > @@ -5834,6 +5834,7 @@ static int select_idle_cpu(struct task_struct *p, struct sched_domain *sd, int t
> >   	s64 delta;
> >   	int this = smp_processor_id();
> >   	int cpu, nr = INT_MAX, si_cpu = -1;
> > +	struct cpumask cpus;
> NAK, you must not put a cpumask on stack.
>
> .

Hi, Peter

ÂÂÂ I saw the same work in select_idle_core, and I was wondering why 
the per_cpu variable was

needed for this yesterday. Now I think I probably understand : cpumask 
may be too large,

putting it on the stack may cause overflow. Is this correct ?

ÂÂÂ I'm sorry I made a mistake like this. I will fix it in v2

ÂÂÂ Thank you very much.


ÂÂÂÂÂÂÂ -- Cheng Jian