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.
> 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);
