On Mon, Apr 19, 2010 at 09:19:38AM -0700, Jeremy Fitzhardinge wrote: > On 04/19/2010 07:26 AM, Glauber Costa wrote: > >> Is the problem that the tscs are starting out of sync, or that they're > >> drifting relative to each other over time? Do the problems become worse > >> the longer the uptime? How large are the offsets we're talking about here? > >> > > The offsets usually seem pretty small, under a microsecond. So I don't think > > it has anything to do with tscs starting out of sync. Specially because the > > delta-based calculation has the exact purpose of handling that case. > > > > So you think they're drifting out of sync from an initially synced > state? If so, what would bound the drift? I think delta calculation introduces errors. Marcelo can probably confirm it, but he has a nehalem with an appearently very good tsc source. Even this machine warps. It stops warping if we only write pvclock data structure once and forget it, (which only updated tsc_timestamp once), according to him. Obviously, we can't do that everywhere. -- 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
