Re: [Qemu-devel] [PATCH 3/3] KVM: use KVM_CAP_MAX_VCPU_ID

[Greg Kurz]

On Fri, 27 May 2016 13:16:49 +0200
Greg Kurz <address@hidden> wrote:

> On Fri, 27 May 2016 13:58:28 +1000
> David Gibson <address@hidden> wrote:
> 
> > On Thu, May 26, 2016 at 10:02:23AM +0200, Greg Kurz wrote:  
> > > As stated in linux/Documentation/virtual/kvm/api.txt:
> > > 
> > > The maximum possible value for max_vcpu_id can be retrieved using the
> > > KVM_CAP_MAX_VCPU_ID of the KVM_CHECK_EXTENSION ioctl() at run-time.
> > > 
> > > If the KVM_CAP_MAX_VCPU_ID does not exist, you should assume that
> > > max_vcpu_id is the same as the value returned from KVM_CAP_MAX_VCPUS.
> > > 
> > > Signed-off-by: Greg Kurz <address@hidden>    
> > 
> > Reviewed-by: David Gibson <address@hidden>
> >   
> 
> Paolo,
> 
> FYI Patch 1/3 was in David's pull request earlier today. It is now upstream.
> 
> You may now apply 2/3 and 3/3.
> 
> Thanks !
> 

Hi Paolo,

Just a friendly reminder. Without this patch, we cannot create more than
128 single-threaded vCPUs on POWER8 if the host has unsplit cores.

Thanks !

--
Greg

> --
> Greg
> 
> > > ---
> > >  kvm-all.c |    8 +++++++-
> > >  1 file changed, 7 insertions(+), 1 deletion(-)
> > > 
> > > diff --git a/kvm-all.c b/kvm-all.c
> > > index e56f38527815..e74e0c6e2352 100644
> > > --- a/kvm-all.c
> > > +++ b/kvm-all.c
> > > @@ -1459,10 +1459,16 @@ static int kvm_max_vcpus(KVMState *s)
> > >      return (ret) ? ret : kvm_recommended_vcpus(s);
> > >  }
> > >  
> > > +static int kvm_max_vcpu_id(KVMState *s)
> > > +{
> > > +    int ret = kvm_check_extension(s, KVM_CAP_MAX_VCPU_ID);
> > > +    return (ret) ? ret : kvm_max_vcpus(s);
> > > +}
> > > +
> > >  bool kvm_vcpu_id_is_valid(int vcpu_id)
> > >  {
> > >      KVMState *s = KVM_STATE(current_machine->accelerator);
> > > -    return vcpu_id >= 0 && vcpu_id < kvm_max_vcpus(s);
> > > +    return vcpu_id >= 0 && vcpu_id < kvm_max_vcpu_id(s);
> > >  }
> > >  
> > >  static int kvm_init(MachineState *ms)
> > >     
> >   
> 
>