On 08/14/2015 06:02 AM, Morten Rasmussen wrote: > To be sure not to break smp_nice, we have defined over-utilization as > when: > > cpu_rq(any)::cfs::avg::util_avg + margin > cpu_rq(any)::capacity > > is true for any cpu in the system. IOW, as soon as one cpu is (nearly) > 100% utilized, we switch to load_avg to factor in priority. > > Now with this definition, we can skip periodic load-balance as no cpu > has an always-running task when the system is not over-utilized. All > tasks will be periodic and we can balance them at wake-up. This > conservative condition does however mean that some scenarios that could > benefit from energy-aware decisions even if one cpu is fully utilized > would not get those benefits. > > For system where some cpus might have reduced capacity on some cpus > (RT-pressure and/or big.LITTLE), we want periodic load-balance checks as > soon a just a single cpu is fully utilized as it might one of those with > reduced capacity and in that case we want to migrate it. > > I haven't found any reasonably easy-to-track conditions that would work > better. Suggestions are very welcome.
Workloads with a single heavy task and many small tasks are pretty common. I'm worried about the single heavy task tripping the over-utilization condition on a b.L system, EAS getting turned off, and small tasks running on big CPUs, leading to an increase in power consumption. Perhaps an extension to the over-utilization logic such as the following could cause big CPUs being saturated by a single task to be ignored? util(cpu X) + margin > capacity(cpu X) && (capacity(cpu X) != max_capacity ? 1 : nr_running(cpu X) > 1) -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
