Re: [Qemu-ppc] [Qemu-devel] [PATCH 1/1] spapr: Ensure CPU cores are added contiguously and removed in LIFO order

[Igor Mammedov]

On Wed, 13 Jul 2016 10:19:00 +0200
Igor Mammedov <address@hidden> wrote:

> On Wed, 13 Jul 2016 09:42:54 +0200
> Igor Mammedov <address@hidden> wrote:
> 
> > On Wed, 13 Jul 2016 12:20:20 +0530
> > Bharata B Rao <address@hidden> 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.  
> CCing Peter for libvirt's opinion on this turn of events
didn't actually CCed him :/

> 
> > 
> >   
> > > Signed-off-by: Bharata B Rao <address@hidden>
> > > ---
> > > 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);    
> > 
> >   
> 
>