Re: [Xen-devel] [PATCH 16/16] xen: sched: implement vcpu hard affinity in Credit2

[Dario Faggioli <dario.faggioli@xxxxxxxxxx>]

On Thu, 2016-03-24 at 15:42 +0000, George Dunlap wrote:
> On Fri, Mar 18, 2016 at 7:06 PM, Dario Faggioli
> <dario.faggioli@xxxxxxxxxx> wrote:
> > 
> > From: Justin Weaver <jtweaver@xxxxxxxxxx>
> > 
> > Signed-off-by: Justin Weaver <jtweaver@xxxxxxxxxx>
> > Signed-off-by: Dario Faggioli <dario.faggioli@xxxxxxxxxx>
> Just checking, are the main changes between this patch and the v4
> that
> Justin posted:
> 
> 1) Moving the "scratch_mask" to a different patch
> 2) The code-cleanups you listed?
> 
Yes, indeed! Sorry for not pointing that out more clearly (e.g., in the
cover letter).

> One rather tangential question...

> > --- a/xen/common/sched_credit2.c
> > +++ b/xen/common/sched_credit2.c
> > @@ -560,8 +590,9 @@ runq_tickle(const struct scheduler *ops,
> > unsigned int cpu, struct csched2_vcpu *
> >          goto tickle;
> >      }
> > 
> > -    /* Get a mask of idle, but not tickled */
> > +    /* Get a mask of idle, but not tickled, that new is allowed to
> > run on. */
> >      cpumask_andnot(&mask, &rqd->idle, &rqd->tickled);
> > +    cpumask_and(&mask, &mask, new->vcpu->cpu_hard_affinity);
> It looks like this uses a cpumask_t on the stack -- can we use
> scratch_mask here, or is there some reason we need to use the local
> variable?
> 
> But that's really something to either add to the previous patch, or
> to
> do in yet a different patch.
> 
It's because that cpumask stack variable is there already, and the
primary purpose of the scratch mask is to avoid _adding_more_ of them.
This is how it has been introduced and used so far in Credit1 and RTDS.

That said, I do agree it can well be used to get rid of some of the
already existing stack variable, but, as you suggest yourself, I'm
thinking about doing this in another patch.

> Acked-by: George Dunlap <george.dunlap@xxxxxxxxxx>
>
Thanks and Regards,
Dario
-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)

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