Re: [Qemu-devel] [PATCH 6/8] spapr: init CPUState->cpu_index with index relative to core-id

[Bharata B Rao <bharata@linux.vnet.ibm.com>]

On Fri, Jul 22, 2016 at 05:14:33PM +1000, David Gibson wrote:
> On Fri, Jul 22, 2016 at 11:40:03AM +0530, Bharata B Rao wrote:
> > On Fri, Jul 22, 2016 at 01:23:01PM +1000, David Gibson wrote:
> > > On Thu, Jul 21, 2016 at 05:54:37PM +0200, Igor Mammedov wrote:
> > > > It will enshure that cpu_index for a given cpu stays the same
> > > > regardless of the order cpus has been created/deleted and so
> > > > it would be possible to migrate QEMU instance with out of order
> > > > created CPU.
> > > > 
> > > > Signed-off-by: Igor Mammedov <imammedo@redhat.com>
> > > 
> > > So, this isn't quite right (it wasn't right in my version either).
> > > 
> > > The problem occurs when smp_threads < kvmppc_smt_threads().  That is,
> > > when the requested threads-per-core is less than the hardware's
> > > maximum number of threads-per-core.
> > > 
> > > The core-id values are assigned essentially as i *
> > > kvmppc_smt_threads(), meaning the patch below will leave gaps in the
> > > cpu_index values and the last ones will exceed max_cpus, causing other
> > > problems.
> > 
> > This would lead to hotplug failures as cpu_dt_id is still being
> > derived from non-contiguous cpu_index resulting in wrong enumeration
> > of CPU nodes in DT.
> 
> Which "This" are you referring to?

:) Gaps in cpu_index values due to which cpu_dt_id gets calculated wrongly.

Regards,
Bharata.