On Wed, 13 Jul 2016 09:42:54 +0200
Igor Mammedov <imamm...@redhat.com> wrote:
> On Wed, 13 Jul 2016 12:20:20 +0530
> Bharata B Rao <bhar...@linux.vnet.ibm.com> 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.
> Adding this limitation looks better than adding migration_id as
> it will allow libvirt to use the current -numa cpus=... while
> doing the same amount of guess work as it does now.
>
> Similar patch for x86 won't be so simple as cpu-add can add cpus
> with gaps (breaking migration at that), so I'd need to keep it
> that way with some compat code, but that shouldn't be issue.
>
And does libvirt take care not to add cpus with gaps ? If so, maybe it
can do the same with PPC, and we'd simply warn the user that migration
is broken if we introduce gaps. Makes sense ?
>
> > Signed-off-by: Bharata B Rao <bhar...@linux.vnet.ibm.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.
> >
> > hw/ppc/spapr_cpu_core.c | 21 ++++++++++++++++++++-
> > 1 file changed, 20 insertions(+), 1 deletion(-)
> >
> > diff --git a/hw/ppc/spapr_cpu_core.c b/hw/ppc/spapr_cpu_core.c
> > index bc52b3c..4bfc96b 100644
> > --- a/hw/ppc/spapr_cpu_core.c
> > +++ b/hw/ppc/spapr_cpu_core.c
> > @@ -126,12 +126,23 @@ static void spapr_core_release(DeviceState *dev, void
> > *opaque)
> > void spapr_core_unplug(HotplugHandler *hotplug_dev, DeviceState *dev,
> > Error **errp)
> > {
> > + sPAPRMachineState *spapr = SPAPR_MACHINE(OBJECT(hotplug_dev));
> > CPUCore *cc = CPU_CORE(dev);
> > sPAPRDRConnector *drc =
> > spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, cc->core_id);
> > sPAPRDRConnectorClass *drck;
> > Error *local_err = NULL;
> > + int smt = kvmppc_smt_threads();
> > + int index = cc->core_id / smt;
> > + int spapr_max_cores = max_cpus / smp_threads;
> > + int i;
> >
> > + for (i = spapr_max_cores - 1; i > index; i--) {
> > + if (spapr->cores[i]) {
> > + error_setg(errp, "core-id %d should be removed first", i *
> > smt);
> > + return;
> > + }
> > + }
> > g_assert(drc);
> >
> > drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> > @@ -214,7 +225,7 @@ void spapr_core_pre_plug(HotplugHandler *hotplug_dev,
> > DeviceState *dev,
> > sPAPRMachineClass *smc = SPAPR_MACHINE_GET_CLASS(OBJECT(hotplug_dev));
> > sPAPRMachineState *spapr = SPAPR_MACHINE(OBJECT(hotplug_dev));
> > int spapr_max_cores = max_cpus / smp_threads;
> > - int index;
> > + int index, i;
> > int smt = kvmppc_smt_threads();
> > Error *local_err = NULL;
> > CPUCore *cc = CPU_CORE(dev);
> > @@ -252,6 +263,14 @@ void spapr_core_pre_plug(HotplugHandler *hotplug_dev,
> > DeviceState *dev,
> > goto out;
> > }
> >
> > + for (i = 0; i < index; i++) {
> > + if (!spapr->cores[i]) {
> > + error_setg(&local_err, "core-id %d should be added first",
> > + i * smt);
> > + goto out;
> > + }
> > + }
> > +
> > out:
> > g_free(base_core_type);
> > error_propagate(errp, local_err);
>
>
