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

[Peter Krempa]

On Tue, Feb 06, 2018 at 11:05:06 +0000, Daniel Berrange wrote:
> 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

No. That's exactly why I've sent this second mail. I don't want to
litter this stuff into the stats method. The stats method should not
care what weirdness is necessary for a given arch.
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