Re: [Xen-devel] [PATCH v3 29/47] xen/sched: introduce unit_runnable_state()

[Jürgen Groß <jgross@xxxxxxxx>]

On 24.09.19 16:45, Jan Beulich wrote:
> On 24.09.2019 16:25, Jürgen Groß wrote:
> > On 23.09.19 17:24, Jan Beulich wrote:
> > > On 14.09.2019 10:52, Juergen Gross wrote:
> > > > Today the vcpu runstate of a new scheduled vcpu is always set to
> > > > "running" even if at that time vcpu_runnable() is already returning
> > > > false due to a race (e.g. with pausing the vcpu).
> > > I can see this part, ...
> > >
> > > > With core scheduling this can no longer work as not all vcpus of a
> > > > schedule unit have to be "running" when being scheduled. So the vcpu's
> > > > new runstate has to be selected at the same time as the runnability of
> > > > the related schedule unit is probed.
> > > ... but I continue having trouble here. If it has been okay to set
> > > a vCPU no longer runnable to "running" nevertheless, why would the
> > > same not be true for schedule units? Part of the problem may be
> > > that ...
> > The difference is the need to drop the scheduling lock for doing the
> > rendezvous. vcpu_sleep() or vcpu_wake() could now interfere with
> > scheduling in a way which was not possible before.
> Ah, right. But this would be worth mentioning explicitly here to
> help readers, wouldn't it? Doesn't need to be more than half a
> sentence ...
Okay.


Juergen


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