Re: [Qemu-devel] [PATCH v4 05/16] pc: enforce adding CPUs contiguously and removing them in opposit order

[Eric Blake <eblake@redhat.com>]

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On 07/14/2016 10:54 AM, Igor Mammedov wrote:

s/opposit/opposite/ in the subject line, but it's already long. I wonder
if you can go shorter, with:

pc: enforce CPU add/remove in contiguous order

> it will still allow us to use cpu_index as migration instance_id
> since when CPUs are added contiguously (from the first to the last)
> and removed in opposite order, cpu_index stays stable and it's
> reproducable on destination side.

s/reproducable/reproducible/

> 
> Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> ---
> While there is work in progress to support migration when there are holes
> in cpu_index range resulting from out-of-order plug or unplug, this patch
> is intended as a last resort if no easy, risk-free and elegant solution
> emerges before 2.7 dev cycle ends.

I'm not too worried about succeeding only on contiguous ids, as that has
been something libvirt has already had to deal with.  But I am a bit
worried about whether it is easy to introspect whether 2.8 adds a way to
hot-plug (or hot-remove) cpus in arbitrary order, with gaps rather than
contiguous ids, especially if the interface does not gain any obvious
parameters.

If we are going to enhance the interface in the future, do we have any
plans how to make it easily detectable which version of the interface we
are working with (contiguous-only, or full power)?

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org


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