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Re: [Xen-devel] [PATCH V2] Xen: support maxvcpus in xm and xl config

On Tue, 2015-12-15 at 15:20 -0700, Jim Fehlig wrote:
> From: Ian Campbell <ian.campbell@xxxxxxxxxx>
> xend prior to 4.0 understands vcpus as maxvcpus and vcpu_avail
> as a bit map of which cpus are online (default is all).
> xend from 4.0 onwards understands maxvcpus as maxvcpus and
> vcpus as the number which are online (from 0..N-1). The
> upstream commit (68a94cf528e6 "xm: Add maxvcpus support")
> claims that if maxvcpus is omitted then the old behaviour
> (i.e. obeying vcpu_avail) is retained, but AFAICT it was not,
> in this case vcpu==maxcpus==online cpus. This is good for us
> because handling anything else would be fiddly.
> This patch changes parsing of the virDomainDef maxvcpus and vcpus
> entries to use the corresponding 'maxvcpus' and 'vcpus' settings
> from xm and xl config. It also drops use of the old Xen 3.x
> 'vcpu_avail' setting.
> The change also removes the maxvcpus limit of MAX_VIRT_VCPUS (since
> maxvcpus is simply a count, not a bit mask), which is particularly
> crucial on ARM where MAX_VIRT_CPUS == 1 (since all guests are
> expected to support vcpu placement, and therefore only the boot
> vcpu's info lives in the shared info page).
> Existing tests adjusted accordingly, and new tests added for the
> 'maxvcpus' setting.
> Signed-off-by: Jim Fehlig <jfehlig@xxxxxxxx>

Acked-by: Ian Campbell <Ian.campbell@xxxxxxxxxx>
Tested-by: Ian Campbell <Ian.campbell@xxxxxxxxxx>
(as far as "domxml-from-native xen-xl" goes, I seem to have another issue
actually starting a domain on ARM, which I'll investigate...)

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