Messages in this thread | | | Date | Sat, 10 Mar 2007 09:51:49 -0600 | From | Nathan Lynch <> | Subject | Re: [PATCH 1/1] hotplug cpu: migrate a task within its cpuset |
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Hi-
Ingo Molnar wrote: > > * Cliff Wickman <cpw@sgi.com> wrote: > > > With this patch, migrate the task to: > > 1) to any cpu on the same node as the disabled cpu, which is both online > > and among that task's cpus_allowed > > 2) to any online cpu within the task's cpuset > > 3) to any cpu which is both online and among that task's cpus_allowed > > > > Diffed against 2.6.21-rc3 (Andrew's current top of tree) > > looks good to me. > > Acked-by: Ingo Molnar <mingo@elte.hu> > > > + /* try to stay on the same cpuset */ > > + if (dest_cpu == NR_CPUS) { > > + p->cpus_allowed = cpuset_cpus_allowed(p); > > + dest_cpu = any_online_cpu(p->cpus_allowed); > > + } > > what's the practical effect of this - when moving the last CPU offline > from a node you got jobs migrated to really alien nodes? Thus i think we > should queue this up for v2.6.21 too, correct? It's a NOP on systems > that do not set up cpusets, so it's low-risk.
See my earlier reply to this patch. Calling cpuset_cpus_allowed (which takes a mutex) here is a bug, since move_task_off_dead_cpu must be called with interrupts disabled.
> btw., unrelated to your patch, there's this bit right after the code > above: > > /* No more Mr. Nice Guy. */ > if (dest_cpu == NR_CPUS) { > rq = task_rq_lock(p, &flags); > cpus_setall(p->cpus_allowed); > dest_cpu = any_online_cpu(p->cpus_allowed); > > out of consistency, shouldnt the cpus_setall() rather be: > > p->cpus_allowed = cpu_possible_map; > > ? It shouldnt make any real difference but it looks more consistent.
The default value of cpus_allowed is CPU_MASK_ALL, I thought -- at least that's what we set init's to early on. Though, as you say, it shouldn't make any difference.
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