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

[Srikar Dronamraju <srikar@linux.vnet.ibm.com>]

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