Re: [PATCH 2/2] nohz: make nohz_full imply isolcpus

[Chris Metcalf]

On 04/03/2015 01:42 PM, Frederic Weisbecker wrote:
> On Fri, Apr 03, 2015 at 12:24:08PM -0400, cmetcalf@xxxxxxxxxx wrote:
> > From: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> >
> > It's not clear that nohz_full is useful without isolcpus also
> > set, since otherwise the scheduler has to run periodically to
> > try to determine whether to steal work from other cores.
> >
> > Signed-off-by: Chris Metcalf <cmetcalf@xxxxxxxxxx>
> I think Rick has a similar patch.

I didn't see anything relevant in linux-next, though I did see 
cpu_isolated_map
made into a public symbol in a recent commit by Rik.

Rik, what's the change you're proposing that's similar to this one? Thanks!

> > ---
> > I am puzzled why this has not been done before, so I suspect
> > there is some argument against it that I am missing, but I
> > wasn't able to turn anything up by searching LKML.
> >
> >   kernel/sched/core.c | 1 +
> >   1 file changed, 1 insertion(+)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index f0f831e8a345..275f12c608f2 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -6836,6 +6836,7 @@ static int init_sched_domains(const struct cpumask *cpu_map)
> >   	doms_cur = alloc_sched_domains(ndoms_cur);
> >   	if (!doms_cur)
> >   		doms_cur = &fallback_doms;
> > +	tick_nohz_full_set_cpus(cpu_isolated_map);
> >   	cpumask_andnot(doms_cur[0], cpu_map, cpu_isolated_map);
> >   	err = build_sched_domains(doms_cur[0], NULL);
> >   	register_sched_domain_sysctl();
> > --
> > 2.1.2

--
Chris Metcalf, EZChip Semiconductor
http://www.ezchip.com

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