RE: [Xen-devel] [PATCH 2/3] xend: Add multiple cpumasks support

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> > Adding support to enable separate masks for each VCPU isn't a bad
idea,
> > but we certainly don't want to break the behaviour of being able to
set
> > the mask for a domain.
> 
> This doesn't break the previous behavior though maybe the description
or
> implementation is misleading.  We may have dropped the behavior over
time
> as I seem to recall having a cpumap_t/cpumask in the domain structure,
> but there isn't a domain-wide cpumask anymore.  Instead there is a
> cpumask per vcpu.  The cpus parameter is used to restrict which
> physical cpus the domains' vcpus' can use.  This is done by mapping
> each vcpu to a value from the list of physical cpus the domain can
> use.  The side-effect of that is that the cpumask of the vcpu has
> only that cpu set, which prevents balancing when using the credit
> scheduler.

The current code doesn't do what the comment in the example config file
says. We should just fix the code to match the comment!

> Are you asking that we introduce in addition to the per-vcpu cpumask
> another domain-wide mask that we would use to further restrict the
vcpu
> masks (think cpus_and(d->affinity, v->affinity))?  And have two config
> variables like below?

There's no need: just set them all vcpus to the same mask.

Thanks,
Ian



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