[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] [Xen-devel] Load calculation refresh in credit2 (was in Re: Questions about the use of idle_vcpu[])
[Changing the title to align with the current topic] On 18/01/16 12:47, Dario Faggioli wrote: > On Mon, 2016-01-18 at 12:37 +0000, George Dunlap wrote: >> On Mon, Jan 18, 2016 at 11:00 AM, Dario Faggioli >> <dario.faggioli@xxxxxxxxxx> wrote: >>>> >>> Credit2, AFAICR, could also avoid _always_ re-setting the timer, >>> but it >>> does need to do that at least a few times, even when idle is >>> selected, >>> because of the dynamic load tracking mechanism it includes. In >>> fact, >>> that is based on a 'decaying average', which in turns relies on >>> csched2_schedule() to run and update the statistics, even when the >>> cpu >>> is idle. If we don't do that, the load tracking mechanism will >>> never >>> see that the cpu (well, it's actually the runqueue) is idle, and >>> the >>> load will never go down! :-/ >> >> I don't think that's true -- it looks like balance_load() will call >> __update_runq_load() on the "other" runqueue before considering it, >> and will also call __update_svc_load() on each vcpu before >> considering >> it. Shouldn't that suffice? >> > Mm... It looks like it should. > > And yet, I observed that 'load not going down' behavior while doing > development for the patch I mentioned, both on Credit2 and Credit (with > patches for extending the load tracking to Credit applied). > > I was, in the same series, also trying to optimize the Credit2's load > balancer a little bit, though, so what I saw may be the effect of some > other change of mine... Hmm... Did you see it when the system was under load, or mostly idle? Load balancing only happens on a reset event; and the frequency of reset events will be CREDIT_INIT / (% utilization); so for a system at 1% utilization that would be once every second. Is that the kind of number you were seeing? Or were you actually seeing idle runqueues not having anything pushed to them *during* a balance for some reason? -George _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxx http://lists.xen.org/xen-devel
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