On 08/15/2012 10:43 PM, Peter Zijlstra wrote: > On Wed, 2012-08-15 at 15:15 +0200, Borislav Petkov wrote: >> On Wed, Aug 15, 2012 at 01:05:38PM +0200, Peter Zijlstra wrote: >>> On Mon, 2012-08-13 at 20:21 +0800, Alex Shi wrote: >>>> Since there is no power saving consideration in scheduler CFS, I has a >>>> very rough idea for enabling a new power saving schema in CFS. >>> >>> Adding Thomas, he always delights poking holes in power schemes. >>> >>>> It bases on the following assumption: >>>> 1, If there are many task crowd in system, just let few domain cpus >>>> running and let other cpus idle can not save power. Let all cpu take the >>>> load, finish tasks early, and then get into idle. will save more power >>>> and have better user experience. >>> >>> I'm not sure this is a valid assumption. I've had it explained to me by >>> various people that race-to-idle isn't always the best thing. It has to >>> do with the cost of switching power states and the duration of execution >>> and other such things. >> >> I think what he means here is that we might want to let all cores on >> the node (i.e., domain) finish and then power down the whole node which >> should bring much more power savings than letting a subset of the cores >> idle. Alex? > > Sure we can do that. > >>> So I'd leave the currently implemented scheme as performance, and I >>> don't think the above describes the current state. >>> >>>> } else if (schedule policy == power) >>>> move tasks from busiest group to >>>> idlest group until busiest is just full >>>> of capacity. >>>> //the busiest group can balance >>>> //internally after next time LB, >>> >>> There's another thing we need to do, and that is collect tasks in a >>> minimal amount of power domains. >> >> Yep. >> >> Btw, what heuristic would tell here when a domain overflows and another >> needs to get woken? Combined load of the whole domain? >> >> And if I absolutely positively don't want a node to wake up, do I >> hotplug its cores off or are we going to have a way to tell the >> scheduler to overcommit the non-idle domains and spread the tasks only >> among them. >> >> I'm thinking of short bursts here where it would be probably beneficial >> to let the tasks rather wait runnable for a while then wake up the next >> node and waste power... > > I was thinking of a utilization measure made of per-task weighted > runnable averages. This should indeed cover that case and we'll overflow > when on average there is no (significant) idle time over a period longer > than the averaging period.
It's also a good idea. :) > > Anyway, I'm not too set on this and I'm very sure we can tweak this ad > infinitum, so starting with something relatively simple that works for > most is preferred. > > As already stated, I think some of the Linaro people actually played > around with something like this based on PJTs patches. Vincent, would you like to introduce more? -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/