linux-kernel - Re: [PATCH v2] sched/fair: Optimize select_idle

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Date:   Fri, 24 Jan 2020 19:02:13 +0530
From:   Srikar Dronamraju <srikar@...ux.vnet.ibm.com>
To:     Ingo Molnar <mingo@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>
Cc:     LKML <linux-kernel@...r.kernel.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Rik van Riel <riel@...riel.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Valentin Schneider <valentin.schneider@....com>,
        Vincent Guittot <vincent.guittot@...aro.org>
Subject: Re: [PATCH v2] sched/fair: Optimize select_idle_core


Hey Peter, Ingo,

* Srikar Dronamraju <srikar@...ux.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@....com>
> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> Signed-off-by: Srikar Dronamraju <srikar@...ux.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