Messages in this thread | | | Date | Fri, 6 Dec 2019 13:46:54 +0530 | From | Srikar Dronamraju <> | Subject | Re: [PATCH] sched/fair: Optimize select_idle_core |
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* 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 and Regards Srikar Dronamraju
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