Re: [Qemu-devel] [QEMU PATCH] kvmclock: advance clock by time window between vm_stop and pre_save

[Radim Krčmář]

2016-11-04 15:07-0200, Marcelo Tosatti:
> On Fri, Nov 04, 2016 at 04:25:23PM +0100, Radim Krčmář wrote:
>> > +        /*
>> > +         * Transition from VM-running to VM-stopped via migration?
>> > +         * Record when the VM was stopped.
>> > +         */
>> > +
>> > +        if (state == RUN_STATE_FINISH_MIGRATE &&
>> > +            !migration_in_postcopy(migrate_get_current())) {
>> > +            clock_gettime(CLOCK_MONOTONIC, &s->t_aftervmstop);
>> 
>> How big (more like small) was the clock delta between here and
>> kvmclock_pre_save with postcopy?
>> 
>> Thanks.
> 
> qemu-system-x86_64: postcopy_ram_supported_by_host: userfaultfd not
> available: Function not implemented
> 
> But should be about the same as precopy+this patch (guess as i don't 
> know the postcopy path).

I was wondering about the improvement we could achieve by not excluding
postcopy from the time fixup.  (i.e. how much time elapses between
pausing and migrating the vm in postcopy)

I would also guess that it is not significant.