Messages in this thread | | | Date | Tue, 10 Jun 2008 11:47:05 -0700 (PDT) | From | David Rientjes <> | Subject | Re: cpusets and kthreads, inconsistent behaviour |
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On Tue, 10 Jun 2008, Max Krasnyansky wrote:
> Basically the issue is that current behaviour of the cpusets is inconsistent > with regards to kthreads. Kthreads inherit cpuset from a parent properly but > they simply ignore cpuset.cpus when their cpu affinity is set/updated. > I think the behaviour must be consistent across the board. cpuset.cpus must > apply to _all_ the tasks in the set, not just some of the tasks. If kthread > must run on the cpus other than current_cpuset.cpus then it should detach from > the cpuset. >
I disagree that a cpuset's set of allowable cpus should apply to all tasks attached to that cpuset. It's certainly beneficial to be able to further constrict the set of allowed cpus for a task using sched_setaffinity().
It makes more sense to argue that for each task p, p->cpus_allowed is a subset of task_cs(p)->cpus_allowed.
> To give you an example kthreads like scsi_eh, kswapd, kacpid, pdflush, > kseriod, etc are all started with cpus_allows=ALL_CPUS even though they > inherit a cpuset from kthreadd. Yes they can moved manually (with > sched_setaffinity) but the behaviour is not consistent, and for no good > reason. kthreads can be stopped/started at any time (module load for example) > which means that the user will have to keep moving them. >
This doesn't seem to be purely a kthread issue. Tasks can be moved to a disjoint set of cpus by any caller to set_cpus_allowed_ptr() in the kernel.
David
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