Re: [Xen-devel] [PATCH v4 20/46] xen: let vcpu_create() select processor

[Dario Faggioli <dfaggioli@xxxxxxxx>]

On Fri, 2019-09-27 at 09:00 +0200, Juergen Gross wrote:
> Today there are two distinct scenarios for vcpu_create(): either for
> creation of idle-domain vcpus (vcpuid == processor) or for creation
> of
> "normal" domain vcpus (including dom0), where the caller selects the
> initial processor on a round-robin scheme of the allowed processors
> (allowed being based on cpupool and affinities).
> 
> Instead of passing the initial processor to vcpu_create() and passing
> on to sched_init_vcpu() let sched_init_vcpu() do the processor
> selection. For supporting dom0 vcpu creation use the node_affinity of
> the domain as a base for selecting the processors. User domains will
> have initially all nodes set, so this is no different behavior
> compared
> to today. In theory this is not guaranteed as vcpus are created only
> with XEN_DOMCTL_max_vcpus being called, but this call is going to be
> removed in future and the toolstack doesn't call
> XEN_DOMCTL_setnodeaffinity before calling XEN_DOMCTL_max_vcpus.
> 
> To be able to use const struct domain * make cpupool_domain_cpumask()
> take a const domain pointer, too.
> 
> A further simplification is possible by having a single function for
> creating the dom0 vcpus with vcpu_id > 0 and doing the required
> pinning
> for all vcpus after that. This allows to make sched_set_affinity()
> private to schedule.c and switch it to sched_units easily. Note that
> this functionality is x86 only.
> 
> Signed-off-by: Juergen Gross <jgross@xxxxxxxx>
> Acked-by: Julien Grall <julien.grall@xxxxxxx>
>
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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