Messages in this thread | | | From | Valentin Schneider <> | Subject | Re: [PATCH v7] sched/fair: Consider cpu affinity when allowing NUMA imbalance in find_idlest_group | Date | Fri, 10 Jun 2022 17:25:34 +0100 |
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On 10/06/22 16:15, Peter Zijlstra wrote: > On Fri, Jun 10, 2022 at 11:55:37AM +0100, Valentin Schneider wrote: >> >> IIUC we want to pay special attention when the task isn't allowed to run on >> all online CPUs, wouldn't the below do that? >> >> !cpumask_subset(cpu_online_mask, p->cpus_ptr) > > At that point we might just as well do the whole cpumask_and() thing, > no? There's not much cost difference between these two operations. >
Yeah, you got a point there.
>> The task affinity can be a superset of the online mask, obvious case is >> init_task's CPU_MASK_ALL, and the above test is still false if both masks >> are equal. >> >> (Additionnaly we could add a step in sched_init() to "properly" initialize >> the init_task mask and remove the NR_CPUS faff). > > I'm confused, NR_CPUS is the right value for CPU_MASK_ALL.
Right, I meant to make the mask match cpu_online_mask from the get go, but now that I allocate a few more neurons thinking about it it looks like a can of worms; we'd have to do that after smp_init() to see which CPUs we actually onlined, and by then we have already forked around.
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