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SubjectRe: [PATCH v2] sched/fair: Optimize select_idle_core

Hey Peter, Ingo,

* Srikar Dronamraju <srikar@linux.vnet.ibm.com> [2019-12-06 22:54:22]:

> 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. Also while clearing the cpumask, bits
> of all CPUs of a core can be cleared in one-shot.
>
> Collecting ticks on a Power 9 SMT 8 system around select_idle_core
> while running schbench shows us
>
> (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%
>
>
> Reviewed-by: Valentin Schneider <valentin.schneider@arm.com>
> Reviewed-by: Vincent Guittot <vincent.guittot@linaro.org>
> Signed-off-by: Srikar Dronamraju <srikar@linux.vnet.ibm.com>
> ---
> Changelog v1->v2:
> Updated patch description with measurements made from a debug patch.
>
> kernel/sched/fair.c | 6 ++++--
> 1 file changed, 4 insertions(+), 2 deletions(-)

Do you have any comments or improvements to be done for this patch?

--
Thanks and Regards
Srikar Dronamraju

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