On Fri, 22 Jul 2016 17:14:33 +1000 David Gibson <da...@gibson.dropbear.id.au> 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 <imamm...@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? > > > > > For -smp 8,threads=4 we see the following CPU nodes in DT > > > > PowerPC,POWER8@0 PowerPC,POWER8@10 > > > > which otherwise should have been > > > > PowerPC,POWER8@0 PowerPC,POWER8@8 > > > > The problem manifests as drmgr failure. > > > > Greg's patchset that moved cpu_dt_id setting to machine code and that > > derived cpu_dt_id from core-id for sPAPR would be needed to fix this > > I guess. > > No, it shouldn't be necessary to fix it. But we certainly do want to > clean this stuff up. I'm not terribly convinced by the current > approach in Greg's series though. I'd actually prefer to remove > cpu_dt_id from the cpustate entirely and instead work it out from the That was the initial plan for my series :) > (now stable) cpu index when we go to construct the device tree. > Patch 5/8 provides a stable cpu_index for the pc machine type out of the index in possible_cpus[]. Since we also store cores and threads in fixed size arrays, we could easily follow the same logic: index_of_core_in_spapr_cores * smp_threads + index_of_thread_in_core_threads Cheers. -- Greg
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