From mboxrd@z Thu Jan 1 00:00:00 1970 From: peterz@infradead.org (Peter Zijlstra) Date: Wed, 4 Jun 2014 11:23:13 +0200 Subject: [PATCH v2 08/11] sched: get CPU's activity statistic In-Reply-To: <20140604085542.GH29593@e103034-lin> References: <1400860385-14555-1-git-send-email-vincent.guittot@linaro.org> <1400860385-14555-9-git-send-email-vincent.guittot@linaro.org> <20140528121001.GI19967@e103034-lin> <20140528154703.GJ19967@e103034-lin> <20140603155007.GZ30445@twins.programming.kicks-ass.net> <20140604080809.GK30445@twins.programming.kicks-ass.net> <20140604085542.GH29593@e103034-lin> Message-ID: <20140604092313.GB11096@twins.programming.kicks-ass.net> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Wed, Jun 04, 2014 at 09:55:42AM +0100, Morten Rasmussen wrote: > Both running_avg and runnable_avg are affected by other tasks on the > same cpus, but in different ways. They are equal if you only have one > task on a cpu. If you have more, running_avg will give you the true > requirement of the tasks until the cpu is fully utilized. At which point > the task running_avg will drop if you add more tasks (the unweighted sum > of task running_avgs remains constant). > > runnable_avg on the other hand, might be affected as soon as you have > two task running on the same cpu if they are runnable at the same time. > That isn't necessarily a bad thing for load-balancing purposes, because > tasks that are runnable at the same time are likely to be run more > efficiently by placing them on different cpus. You might view as at sort > of built in concurrency factor, somewhat similar to what Yuyang is > proposing. runnable_avg increases rapidly when the cpu is over-utilized. Agreed. > > I'm not sure I see how 100% is possible, but yes I agree that runnable > > can indeed be inflated due to this queueing effect. > > You should only be able to get to 75% worst case for runnable_avg for > that example. The total running_avg is 50% no matter if the tasks > overlaps or not. Yes, 75% is what I ended up with. > f you had five tasks on one cpu that each have a 25% requirement you can > get individual task runnable_avgs of up to 100% (cpu unweighted > runnable_load_avg can get up 500%, I think), but the task running_avgs > would be 20% each (total of 100%). Yeah, more or less so indeed. I had not considered the queueing effects on runnable_avg yesterday, so good that that got raised. That does indeed invalidate my: runnable - running := extra cpu required thing. It ends up being the extra cpu required for 0 latency but gobs of idle time, which is something else entirely. -------------- next part -------------- A non-text attachment was scrubbed... Name: not available Type: application/pgp-signature Size: 836 bytes Desc: not available URL: