Re: [Xen-devel] [PATCH v2 2/2] xen: merge temporary vcpu pinning scenarios

[Juergen Gross <jgross@xxxxxxxx>]

On 24.07.19 12:07, Jan Beulich wrote:
> On 23.07.2019 20:25, Juergen Gross wrote:
> > Today there are two scenarios which are pinning vcpus temporarily to
> > a single physical cpu:
> >
> > - wait_event() handling
> > - vcpu_pin_override() handling
> >
> > Each of those cases are handled independently today using their own
> > temporary cpumask to save the old affinity settings.
> >
> > The two cases can be combined as the first case will only pin a vcpu to
> > the physical cpu it is already running on, while vcpu_pin_override() is
> > allowed to fail.
> >
> > So merge the two temporary pinning scenarios by only using one cpumask
> > and a per-vcpu bitmask for specifying which of the scenarios is
> > currently active (they are allowed to nest).
> Hmm, "nest" to me means LIFO-like behavior, but the logic is more relaxed
> afaict.
Okay, will rephrase.

> > @@ -1267,7 +1284,8 @@ ret_t do_sched_op(int cmd, XEN_GUEST_HANDLE_PARAM(void) 
> > arg)
> >           if ( copy_from_guest(&sched_pin_override, arg, 1) )
> >               break;
> >    
> > -        ret = vcpu_pin_override(current, sched_pin_override.pcpu);
> > +        cpu = sched_pin_override.pcpu < 0 ? NR_CPUS : sched_pin_override.pcpu;
> I don't think you mean the caller to achieve the same effect by both
> passing in a negative value or NR_CPUS - it should remain to be just
> negative values which clear the override.
Okay.


Juergen

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