Messages in this thread | | | Subject | Re: Q: select_fallback_rq() && cpuset_lock() | From | Peter Zijlstra <> | Date | Thu, 11 Mar 2010 16:41:18 +0100 |
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On Thu, 2010-03-11 at 16:22 +0100, Oleg Nesterov wrote: > On 03/11, Oleg Nesterov wrote: > > > > How can we fix this later? Perhaps we can change > > cpuset_track_online_cpus(CPU_DEAD) to scan all affected cpusets and > > fixup the tasks with the wrong ->cpus_allowed == cpu_possible_mask. > > Wait. We need to fix the CPU_DEAD case anyway? > > Hmm. 6ad4c18884e864cf4c77f9074d3d1816063f99cd > "sched: Fix balance vs hotplug race" did s/CPU_DEAD/CPU_DOWN_PREPARE/ > in cpuset_track_online_cpus(). This doesn't look exactly right to me, > we shouldn't do remove_tasks_in_empty_cpuset() at CPU_DOWN_PREPARE > stage, it can fail.
Sure, tough luck for those few tasks.
> Otoh. This means that move_task_of_dead_cpu() can never see the > task without active cpus in ->cpus_allowed, it is called later by > CPU_DEAD. So, cpuset_lock() is not needed at all.
Right,.. so the whole problem is cpumask ops are terribly expensive since we got this CONFIG_CPUMASK_OFFSTACK muck, so we try to reduce these ops in the regular scheduling paths, in the patch you referenced above the tradeof was between fixing the sched_domains up too often vs adding a cpumask_and in a hot-path, guess who won ;-)
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