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

[Michal Privoznik <mprivozn@xxxxxxxxxx>]

On 15.12.2015 23:20, 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>
> ---
> 
> This is a respin of Ian's patch [1] to support parsing/formatting of the
> 'maxvcpus' xm and xl config setting. It goes a bit further and removes
> the old Xen 3.x 'vcpu_avail' setting and lifts the maxvcpus limit of
> MAX_VIRT_CPUS entirely.
> 
> The patch is based on my recent series [2] removing xend config version from
> the codebase.
> 
> [1] https://www.redhat.com/archives/libvir-list/2015-November/msg01155.html
> [2] https://www.redhat.com/archives/libvir-list/2015-December/msg00616.html
> 
> 
>  src/xenconfig/xen_common.c                    | 25 +++++++++++----------
>  tests/xlconfigdata/test-paravirt-maxvcpus.cfg | 13 +++++++++++
>  tests/xlconfigdata/test-paravirt-maxvcpus.xml | 28 ++++++++++++++++++++++++
>  tests/xlconfigtest.c                          |  1 +
>  tests/xmconfigdata/test-paravirt-maxvcpus.cfg | 13 +++++++++++
>  tests/xmconfigdata/test-paravirt-maxvcpus.xml | 31 
> +++++++++++++++++++++++++++
>  tests/xmconfigdata/test-paravirt-vcpu.cfg     |  4 ++--
>  tests/xmconfigtest.c                          |  1 +
>  8 files changed, 101 insertions(+), 15 deletions(-)

ACK

Michal

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