Re: [Qemu-devel] [QEMU patch 2/2] kvm: allow configuration of tsc deadline timer advancement

[Marcelo Tosatti <mtosatti@redhat.com>]

On Wed, Dec 10, 2014 at 06:01:21PM +0100, Paolo Bonzini wrote:
> 
> 
> On 10/12/2014 17:23, Marcelo Tosatti wrote:
> > Add machine option and QMP commands to configure TSC deadline
> > timer advancement.
> > 
> > Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>
> > 
> > ---
> >  monitor.c         |   15 ++++++++++
> >  qapi-schema.json  |   29 +++++++++++++++++++
> >  qmp-commands.hx   |   48 ++++++++++++++++++++++++++++++++
> >  target-i386/kvm.c |   80 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  vl.c              |    4 ++
> >  5 files changed, 176 insertions(+)
> > 
> > Index: qemu.tscdeadline/qapi-schema.json
> > ===================================================================
> > --- qemu.tscdeadline.orig/qapi-schema.json
> > +++ qemu.tscdeadline/qapi-schema.json
> > @@ -3515,3 +3515,32 @@
> >  # Since: 2.1
> >  ##
> >  { 'command': 'rtc-reset-reinjection' }
> > +
> > +##
> > +# @set-lapic-tscdeadline-advance
> > +#
> > +# This command sets the TSC deadline timer advancement.
> > +# This value will be subtracted from the expiration time
> > +# of the high resolution timer which emulates
> > +# TSC deadline timer.
> > +#
> > +# Useful to achieve low timer latencies.
> > +#
> > +# Only supported by KVM acceleration.
> > +#
> > +# Since: 2.3
> > +##
> > +{ 'command': 'set-lapic-tscdeadline-advance',
> > +  'data': { 'advance':'int' }
> > +}
> > +
> > +##
> > +# @get-lapic-tscdeadline-advance
> > +#
> > +# This command gets the TSC deadline timer advancement.
> > +#
> > +# Only supported by KVM acceleration.
> > +#
> > +# Since: 2.3
> > +##
> > +{ 'command': 'get-lapic-tscdeadline-advance', 'returns': 'int' }
> 
> Please add an object property to the x86 CPU object.  It can then be
> configured with "-global" on the command line.

Don't want to allow individual values for different CPUs. 
It is a per-VM property.

Is it still appropriate to use an object property of the 
CPU object?

> 
> > +    ret = kvm_vm_ioctl(s, KVM_SET_TSCDEADLINE_ADVANCE, &adv);
> > +    if (ret < 0) {
> > +        return ret;
> > +    }
> 
> Please use KVM_GET/SET_ONE_REG instead of introducing a new set of ioctls.
> 
> Paolo