Re: [PATCH v2] KVM: x86: update masterclock values on TSC writes

[Paolo Bonzini <pbonzini@redhat.com>]

On 05/11/2014 19:19, Marcelo Tosatti wrote:
>>> > > +	 * If the vcpus have matched TSCs and host clocksource is TSC,
>>> > > +	 * perform request to enable masterclock.
>>> > > +	 *
>>> > > +	 * If the masterclock is enabled, perform request to update
>>> > > +	 * masterclock values.
>>> > > +	 */
>>> > > +	if ((vcpus_matched && gtod->clock.vclock_mode == VCLOCK_TSC) ||
>>> > > +	     ka->use_master_clock)
>> > 
>> > This is not an explanation, it is a literal translation from C to
>> > English. :)  Can you also explain the why, especially for the first half
>> > of the condition?
>> > 
>> > Paolo
> The comment on top of pvclock_update_vm_gtod_copy says:
> 
> "Rely on synchronization of host TSCs and guest TSCs for monotonicity."
> 
> Then with this patch
> 
> "If the vcpus have matched TSCs and host clocksource is TSC"
> 
> Is it sufficient to add
> 
> "Masterclock requires synchronized guest TSC and host clocksource TSC" 
> to this patch?

Got it now, thanks.  I think I misread one "enable" as "update" in your
comment, sorry.  I'll apply v2 tomorrow.

Paolo