Re: [Qemu-devel] [PATCH 1/1] spapr: Ensure CPU cores are added contiguously and removed in LIFO order

[David Gibson]

On Thu, Jul 14, 2016 at 10:27:15AM +0200, Igor Mammedov wrote:
> On Thu, 14 Jul 2016 10:51:27 +1000
> David Gibson <address@hidden> wrote:
> 
> > On Wed, Jul 13, 2016 at 12:20:20PM +0530, Bharata B Rao wrote:
> > > If CPU core addition or removal is allowed in random order leading to
> > > holes in the core id range (and hence in the cpu_index range), migration
> > > can fail as migration with holes in cpu_index range isn't yet handled
> > > correctly.
> > > 
> > > Prevent this situation by enforcing the addition in contiguous order
> > > and removal in LIFO order so that we never end up with holes in
> > > cpu_index range.
> > > 
> > > Signed-off-by: Bharata B Rao <address@hidden>
> > > ---
> > > 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.  
> > 
> > Applied to ppc-for-2.7.  We can revert it once the problems with
> > cpu_index are sorted out.
> You'd need to add machine type specific compat option here,
> so that new-qemu -M 2.7 wouldn't allow out of order too and
> could be migrated to old-qemu -M 2.7

Hmm, do we care about migration from newer back to older versions of
qemu upstream?  If so, then I guess we do need this option.  Though
strictly we don't need it until we actually do allow any-order
hotplug.

-- 
David Gibson                    | I'll have my music baroque, and my code
david AT gibson.dropbear.id.au  | minimalist, thank you.  NOT _the_ _other_
                                | _way_ _around_!
http://www.ozlabs.org/~dgibson

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