On Wed, Jan 07, 2009 at 08:28:09AM +0100, Peter Zijlstra wrote: > On Wed, 2009-01-07 at 04:00 +0100, Nick Piggin wrote: > > On Wed, Jan 07, 2009 at 12:16:03AM +0100, Peter Zijlstra wrote: > > > > > > > > But doesn't scheduler tick advance the rq->clock? Why do the others > > > > need to fiddle with a remote runqueue's clock? When that cpu starts > > > > taking ticks again, it will update it's rq->clock field and start the > > > > processes. I guess I am a lot underinformed about the new scheduler > > > > design. > > > > > > We try to do better than tick based time accounting these days. > > > > But if you contain the drift to within one tick, it shouldn't be much > > problem to just truncate negative deltas I would have thought? The > > time between events on different CPUs is pretty fuzzy at the ns level > > anyway, I think ;) > > That's basically what the HAVE_UNSTABLE_SCHED_CLOCK code does. It takes > a tick timestamp and tries to improve on that by using strict per cpu > sched_clock() deltas. > > What we do to obtain remote time, is basically calculate local time and > pull remote time fwd if that was behind. > > While doing that, it filters out any backward motion and large fwd leaps > so as to stay no worse than a jiffie clock. OK, that's good. I guess the optimisations to remove that code should have been called HAVE_STABLE_SCHED_CLOCK and have archs turn it on on a case by case basis. -- To unsubscribe from this list: send the line "unsubscribe linux-ia64" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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