Messages in this thread | | | From | Vincent Guittot <> | Date | Fri, 6 Dec 2019 14:27:17 +0100 | Subject | Re: [PATCH] sched/fair: Optimize select_idle_core |
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On Fri, 6 Dec 2019 at 09:17, Srikar Dronamraju <srikar@linux.vnet.ibm.com> wrote: > > * Vincent Guittot <vincent.guittot@linaro.org> [2019-12-05 19:52:40]: > > > On Thu, 5 Dec 2019 at 18:52, Srikar Dronamraju > > <srikar@linux.vnet.ibm.com> wrote: > > > > > > * Vincent Guittot <vincent.guittot@linaro.org> [2019-12-05 18:27:51]: > > > > > > > Hi Srikar, > > > > > > > > On Thu, 5 Dec 2019 at 18:23, Srikar Dronamraju > > > > <srikar@linux.vnet.ibm.com> wrote: > > > > > > > > > > Currently we loop through all threads of a core to evaluate if the core > > > > > is idle or not. This is unnecessary. If a thread of a core is not > > > > > idle, skip evaluating other threads of a core. > > > > > > > > I think that the goal is also to clear all CPUs of the core from the > > > > cpumask of the loop above so it will not try the same core next time > > > > > > > > > > > > > > > That goal we still continue to maintain by the way of cpumask_andnot. > > > i.e instead of clearing CPUs one at a time, we clear all the CPUs in the > > > core at one shot. > > > > ah yes sorry, I have been to quick and overlooked the cpumask_andnot line > > > > Just to reiterate why this is necessary. > Currently, even if the first thread of a core is not idle, we iterate > through all threads of the core and individually clear the CPU from the core > mask. > > Collecting ticks on a Power 9 SMT 8 system around select_idle_core > while running schbench shows us that > > (units are in ticks, hence lesser is better) > Without patch > N Min Max Median Avg Stddev > x 130 151 1083 284 322.72308 144.41494 > > > With patch > N Min Max Median Avg Stddev Improvement > x 164 88 610 201 225.79268 106.78943 30.03%
Thanks for the figures. Might be good to include them in the commit message
Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> > -- > Thanks and Regards > Srikar Dronamraju >
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