[libvirt] [PATCH] qemu: Limit refresh of CPU halted state to s390

[Daniel P. Berrangé]

On Tue, Feb 06, 2018 at 12:00:31PM +0100, Peter Krempa wrote:
> On Tue, Feb 06, 2018 at 11:55:07 +0100, Peter Krempa wrote:
> > On Tue, Feb 06, 2018 at 11:18:56 +0100, Viktor Mihajlovski wrote:
> > > Refreshing the halted state can cause VM performance issues. Since
> > > s390 is currently the only architecture with a known interest in
> > > the halted state, we're avoiding to call QEMU on other platforms.
> > > 
> > > Signed-off-by: Viktor Mihajlovski <mihajlov at linux.vnet.ibm.com>
> > > ---
> > >  src/qemu/qemu_domain.c | 4 ++++
> > >  1 file changed, 4 insertions(+)
> > > 
> > > diff --git a/src/qemu/qemu_domain.c b/src/qemu/qemu_domain.c
> > > index df433c2..d2c833f 100644
> > > --- a/src/qemu/qemu_domain.c
> > > +++ b/src/qemu/qemu_domain.c
> > > @@ -8634,6 +8634,10 @@ qemuDomainRefreshVcpuHalted(virQEMUDriverPtr driver,
> > >      if (vm->def->virtType == VIR_DOMAIN_VIRT_QEMU)
> > >          return 0;
> > >  
> > > +    /* Only supported on s390(x) */
> 
> This would also benefit from a more thorough comment.
> 
> > > +    if (!ARCH_IS_S390(vm->def->os.arch))
> > > +        return 0;
> > 
> > I think we also should remove the 'halted' field from the stats output
> > if the information was not gathered at all, since it would falsely reply
> > that the cpu is not halted all the time.
> 
> Also to do so you'll probably need to convert the 'halted' bool to a
> tristate, so that the logic determining whether the field should be used
> or not is not present in the stats code but it's in the refresh code as
> you've added it.

Or the lazy way out is to just add ARCH_IS_S390() check in the stats
method too


Regards,
Daniel
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