[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] Questions about the use of idle_vcpu[]
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: > > >Â > > 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.ÂÂShouldn'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... I'll have a go at just disabling the periodic scheduler activation when cpu is idle in the current code, and if it works, I'll send a patch. Thanks and Regards, Dario -- <<This happens because I choose it to happen!>> (Raistlin Majere) ----------------------------------------------------------------- Dario Faggioli, Ph.D, http://about.me/dario.faggioli Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK) Attachment:
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