On Thu, Sep 24, 2020 at 12:53:25PM +0100, Valentin Schneider wrote: > > @@ -1830,8 +1892,19 @@ static int migration_cpu_stop(void *data > > */ > > void set_cpus_allowed_common(struct task_struct *p, const struct cpumask > > *new_mask, u32 flags) > > { > > - cpumask_copy(&p->cpus_mask, new_mask); > > - p->nr_cpus_allowed = cpumask_weight(new_mask); > > + if (flags & SCA_MIGRATE_DISABLE) { > > + p->cpus_ptr = new_mask; > > + p->nr_cpus_allowed = 1; > > + return; > > + } > > + > > + if (flags & SCA_MIGRATE_ENABLE) > > + p->cpus_ptr = &p->cpus_mask; > > There's that check in __set_cpus_allowed_ptr() that new_mask *must* be > p->cpus_mask when SCA_MIGRATE_ENABLE; that means we could mayhaps shuffle > that to: > > --- > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 7cb13df48366..e0e4e42c5e32 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -1892,18 +1892,14 @@ static int migration_cpu_stop(void *data) > */ > void set_cpus_allowed_common(struct task_struct *p, const struct cpumask > *new_mask, u32 flags) > { > + if (flags & (SCA_MIGRATE_DISABLE | SCA_MIGRATE_ENABLE)) > p->cpus_ptr = new_mask; > else > cpumask_copy(&p->cpus_mask, new_mask); > > + if (flags & SCA_MIGRATE_DISABLE) > + p->nr_cpus_allowed = 1; > + else if (p->cpus_ptr == &p->cpus_mask) > p->nr_cpus_allowed = cpumask_weight(p->cpus_ptr); > }
I'm thinking we should let nr_cpus_allowed reflect ->cpus_mask unconditionally. See these emails: https://lkml.kernel.org/r/20200923170809.gy1362...@hirez.programming.kicks-ass.net https://lkml.kernel.org/r/20200924082717.ga1362...@hirez.programming.kicks-ass.net Basically we want to keep migrate_disable() tasks elegible for migration/PULL. But yes, I think that function can be simplified.