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

[Ian Campbell <ian.campbell@xxxxxxxxxx>]

On Wed, 2015-12-16 at 10:11 +0000, Ian Campbell wrote:
> 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...)

Turned out to be a mismatch between my build-time and run-time libxl
versions, fixed by a clean rebuild. So that's a full Tested-by.

I noticed that the newer cmdline= (inplace of root=+extra= etc) wasn't
supported. I'll knock something up.

Ian.

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