Re: [Xen-devel] [PATCH] xen/sched: fix a potential issue with core scheduling

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Fri, 2019-11-08 at 07:57 +0100, Juergen Gross wrote:
> cpupool_online_cpumask() is used by credit and rt scheduler. It
> returns
> all the cpus of a cpupool or all online cpus in case no cpupool is
> specified.
> 
> The "no cpupool" case can be dropped, as no scheduler other than the
> init scheduler will ever work on cpus not associated with any
> cpupool.
> 
Yes, this is a cool thing about having the init cpupool/idle scheduler
in place. It's even cooler in Credit2, where it will allow us to drop
some of the cpumask_and() cpumask_or() operations.

It's the reason why, even before core scheduling, I was considering
doing an idle scheduler myself.

I'll get to write that patch (the one for Credit2, I mean) at some
point. :-)

> As the individual schedulers should only ever work on scheduling
> resources instead of individual cpus, their cpupool_online_cpumask()
> use should be replaced by cpupool->res_valid.
> 
> Note that only with core scheduling active this might result in
> potential problems, as with cpu scheduling both masks are identical.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
>
Reviewed-by: Dario Faggioli <dfaggioli@xxxxxxxx>

Regards
-- 
Dario Faggioli, Ph.D
http://about.me/dario.faggioli
Virtualization Software Engineer
SUSE Labs, SUSE https://www.suse.com/
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