Re: [PATCH 3/3] kmod: Remove unecessary explicit wide CPU affinity setting

[Oleg Nesterov]

On 07/07, Frederic Weisbecker wrote:
>
> On Tue, Jul 07, 2015 at 06:30:30PM +0200, Oleg Nesterov wrote:
> >
> > > Not only useless it even breaks nohz full. The housekeeping work
> > > (general kernel internal code that user doesn't care much about) is
> > > handled by a reduced set of CPUs in nohz full, precisely those that are
> > > not included by nohz_full= kernel parameters. For example unbound
> > > workqueues are handled by housekeeping CPUs.
> >
> > Confused... I do not see how workqueue_attrs->cpumask can depend on
> > tick_nohz_full_mask or housekeeping_mask. Could you explain?
>
> People who want CPU isolation will likely write
> /sys/devices/virtual/workqueue/cpumask to a reduced set of CPUs, typically
> CPU 0 that is used for housekeeping in nohz full.

Well, khelper_wq is not WQ_SYSFS, so I am not sure this is possible.

But this doesn't really matter, people can change cpu affinity. But
"workqueues are handled by housekeeping CPUs" doesn't look right.

> In fact we should add the code which initialize wq_unbound_cpumask
> to housekeeping_mask automatically.

Perhaps, but until then the changelog above looks really confusing,
as if workqueue.c already does this automagically ;)

Oleg.

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