On Tue, Dec 08, 2020 at 10:57:29AM +0100, Dietmar Eggemann wrote: > On 07/12/2020 10:15, Mel Gorman wrote: > > After select_idle_sibling, p->recent_used_cpu is set to the > > new target. However on the next wakeup, prev will be the same as > > I'm confused here. Isn't current->recent_used_cpu set to 'cpu = > smp_processor_id()' after sis()? Looking at v5.10-rc6.
If you are referring to this; if (want_affine) current->recent_used_cpu = cpu; then it gets removed by the path. That replaces recent_used_cpu with the wakers CPU which still works but the hit rate is lower. > > [...] > > > diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c > > index 23934dbac635..01b38fc17bca 100644 > > --- a/kernel/sched/fair.c > > +++ b/kernel/sched/fair.c > > @@ -6274,6 +6274,7 @@ static int select_idle_sibling(struct task_struct *p, > > int prev, int target) > > > > /* Check a recently used CPU as a potential idle candidate: */ > > recent_used_cpu = p->recent_used_cpu; > > + p->recent_used_cpu = prev; > > if (recent_used_cpu != prev && > > recent_used_cpu != target && > > cpus_share_cache(recent_used_cpu, target) && > > p->recent_used_cpu is already set to prev in this if condition. > That can be removed as redundant, I'll fix it. -- Mel Gorman SUSE Labs