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SubjectRe: [PATCH 2/2] cpusets: update tasks' cpus_allowed and mems_allowed after CPU/NODE offline/online
On Wed, 4 Jun 2008, Paul Jackson wrote:

> Do we need a new PF_* flag for this? Perhaps one can test for this
> by examining the currently available properties of tasks. Would it
> be sufficient to look for kernel threads (NULL mm_struct) whose
> cpus_allowed is a strict subset of the online CPUs?
>

That would only identify kthreads that have been created with a subsequent
call to set_cpus_allowed() or kthread_bind().

The PF_CPU_BOUND change targets only the latter since there are kthreads,
such as kstopmachine, that can continue to manipulate their cpus_allowed
during their lifetime.

Other kthreads such as the scheduler migration thread and soft lockup
watchdog thread, however, always stay bound to a single cpu by use of
kthread_bind(). These are the tasks that get the PF_CPU_BOUND flag and
cannot be rebound via set_cpus_allowed() because of their negative
effects.

David


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