Re: [Qemu-ppc] [RFC PATCH v3 20/24] spapr: CPU hot unplug support

[Bharata B Rao]

On Tue, May 05, 2015 at 05:28:38PM +1000, David Gibson wrote:
> On Fri, Apr 24, 2015 at 12:17:42PM +0530, Bharata B Rao wrote:
> > Support hot removal of CPU for sPAPR guests by sending the hot unplug
> > notification to the guest via EPOW interrupt. Release the vCPU object
> > after CPU hot unplug so that vCPU fd can be parked and reused.
> > 
> > Signed-off-by: Bharata B Rao <address@hidden>
> > ---
> >  hw/ppc/spapr.c              | 101 
> > +++++++++++++++++++++++++++++++++++++++++++-
> >  target-ppc/translate_init.c |  10 +++++
> >  2 files changed, 110 insertions(+), 1 deletion(-)
> > 
> > diff --git a/hw/ppc/spapr.c b/hw/ppc/spapr.c
> > index 9b0701c..910a50f 100644
> > --- a/hw/ppc/spapr.c
> > +++ b/hw/ppc/spapr.c
> > @@ -1481,6 +1481,12 @@ static void spapr_cpu_init(PowerPCCPU *cpu)
> >      qemu_register_reset(spapr_cpu_reset, cpu);
> >  }
> >  
> > +static void spapr_cpu_destroy(PowerPCCPU *cpu)
> > +{
> > +    xics_cpu_destroy(spapr->icp, cpu);
> > +    qemu_unregister_reset(spapr_cpu_reset, cpu);
> > +}
> > +
> >  /* pSeries LPAR / sPAPR hardware init */
> >  static void ppc_spapr_init(MachineState *machine)
> >  {
> > @@ -1883,6 +1889,24 @@ static void 
> > *spapr_populate_hotplug_cpu_dt(DeviceState *dev, CPUState *cs,
> >      return fdt;
> >  }
> >  
> > +static void spapr_cpu_release(DeviceState *dev, void *opaque)
> > +{
> > +    CPUState *cs;
> > +    int i;
> > +    int id = ppc_get_vcpu_dt_id(POWERPC_CPU(CPU(dev)));
> > +
> > +    for (i = id; i < id + smp_threads; i++) {
> > +        CPU_FOREACH(cs) {
> > +            PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +
> > +            if (i == ppc_get_vcpu_dt_id(cpu)) {
> > +                spapr_cpu_destroy(cpu);
> > +                cpu_remove(cs);
> > +            }
> > +        }
> > +    }
> > +}
> > +
> >  static void spapr_cpu_plug(HotplugHandler *hotplug_dev, DeviceState *dev,
> >                              Error **errp)
> >  {
> > @@ -1970,6 +1994,59 @@ static void spapr_cpu_plug(HotplugHandler 
> > *hotplug_dev, DeviceState *dev,
> >      return;
> >  }
> >  
> > +static int spapr_cpu_unplug(Object *obj, void *opaque)
> > +{
> > +    Error **errp = opaque;
> > +    DeviceState *dev = DEVICE(obj);
> > +    CPUState *cs = CPU(dev);
> > +    PowerPCCPU *cpu = POWERPC_CPU(cs);
> > +    int id = ppc_get_vcpu_dt_id(cpu);
> > +    int smt = kvmppc_smt_threads();
> > +    sPAPRDRConnector *drc =
> > +        spapr_dr_connector_by_id(SPAPR_DR_CONNECTOR_TYPE_CPU, id);
> > +    sPAPRDRConnectorClass *drck;
> > +    Error *local_err = NULL;
> > +
> > +    /*
> > +     * SMT threads return from here, only main thread (core) will
> > +     * continue and signal hot unplug event to the guest.
> > +     */
> > +    if ((id % smt) != 0) {
> > +        return 0;
> > +    }
> 
> As with the in-plug side couldn't this be done more naturally by
> attaching this function to the cpu core object rather than the thread?

When I switch to core level addition in the next version, I will see
how best this can be handled.

> 
> > +    g_assert(drc);
> > +
> > +    drck = SPAPR_DR_CONNECTOR_GET_CLASS(drc);
> > +    drck->detach(drc, dev, spapr_cpu_release, NULL, &local_err);
> > +    if (local_err) {
> > +        error_propagate(errp, local_err);
> > +        return -1;
> > +    }
> > +
> > +    /*
> > +     * In addition to hotplugged CPUs, send the hot-unplug notification
> > +     * interrupt to the guest for coldplugged CPUs started via -device
> > +     * option too.
> > +     */
> > +    spapr_hotplug_req_remove_event(drc);
> 
> Um.. doesn't the remove notification need to go *before* the
> "physical" unplug?  Along with a wait for acknowledgement from the
> guest?

If I am reading it right, PCI hotplug is also following the same order
(detach followed by guest notification).

Let me experiment with this in the next version.

Regards,
Bharata.