Re: [PATCH 8/8] sched: Relax the set_cpus_allowed_ptr() semantics

[Peter Zijlstra]

On Sat, Jan 16, 2021 at 10:39:03PM +0800, Lai Jiangshan wrote:
> On Sat, Jan 16, 2021 at 7:43 PM Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote:
> >
> > Now that we have KTHREAD_IS_PER_CPU to denote the critical per-cpu
> > tasks to retain during CPU offline, we can relax the warning in
> > set_cpus_allowed_ptr(). Any spurious kthread that wants to get on at
> > the last minute will get pushed off before it can run.
> >
> > While during CPU online there is no harm, and actual benefit, to
> > allowing kthreads back on early, it simplifies hotplug code.
> >
> > Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx>
> 
> Thanks!
> 
> Relaxing set_cpus_allowed_ptr() was also one of the choices I listed,
> which can really simplify hotplug code in the workqueue and may be
> other hotplug code.

Indeed you did. Having that KTHREAD_IS_PER_CPU for the offline side of
things made it possible to relax (as per the Changelog above).

> Reviewed-by: Lai jiangshan <jiangshanlai@xxxxxxxxx>

Thanks!