On Thu, Oct 15, 2009 at 09:46:52AM +0900, Avi Kivity wrote: > On 10/13/2009 09:46 PM, Glauber Costa wrote: >> On Tue, Oct 13, 2009 at 03:31:08PM +0300, Avi Kivity wrote: >> >>> On 10/13/2009 03:28 PM, Glauber Costa wrote: >>> >>>> >>>>> Do we want an absolute or relative adjustment? >>>>> >>>>> >>>> What exactly do you mean? >>>> >>>> >>> Absolute adjustment: clock = t >>> Relative adjustment: clock += t >>> >> The delta is absolute, but the adjustment in the clock is relative. >> >> So we pick the difference between what userspace is passing us and what >> we currently have, then relatively adds up so we can make sure we won't >> go back or suffer a too big skew. >> > > The motivation for relative adjustment is when you have a jitter > resistant place to gather timing information (like the kernel, which can > disable interrupts and preemption), then pass it on to kvm without > losing information due to scheduling. For migration there is no such > place since it involves two hosts, but it makes sense to support > relative adjustments. Since we added the padding you asked for, we could use that bit of information to define whether it will be a relative or absolute adjustment, then. Right now, I don't see the point of implementing a code path that will be completely untested. I'd leave it this way until someone comes up with a need. -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
