linux-kernel - Re: [PATCH] sched/fair: Clear SMT siblings after determining the core is not idle

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Message-ID: <f31178dd-34e4-0e9d-e8e3-fda396641daf@linux.intel.com>
Date:   Tue, 1 Dec 2020 09:04:06 +0800
From:   "Li, Aubrey" <aubrey.li@...ux.intel.com>
To:     Vincent Guittot <vincent.guittot@...aro.org>,
        Mel Gorman <mgorman@...hsingularity.net>
Cc:     Ingo Molnar <mingo@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Valentin Schneider <valentin.schneider@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sched/fair: Clear SMT siblings after determining the core
 is not idle

On 2020/11/30 22:47, Vincent Guittot wrote:
> On Mon, 30 Nov 2020 at 15:40, Mel Gorman <mgorman@...hsingularity.net> wrote:
>>
>> The clearing of SMT siblings from the SIS mask before checking for an idle
>> core is a small but unnecessary cost. Defer the clearing of the siblings
>> until the scan moves to the next potential target. The cost of this was
>> not measured as it is borderline noise but it should be self-evident.
> 
> Good point

This is more reasonable, thanks Mel.

> 
>>
>> Signed-off-by: Mel Gorman <mgorman@...hsingularity.net>
> 
> Reviewed-by: Vincent Guittot <vincent.guittot@...aro.org>
> 
>> ---
>>  kernel/sched/fair.c | 3 ++-
>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>
>> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
>> index 0d54d69ba1a5..d9acd55d309b 100644
>> --- a/kernel/sched/fair.c
>> +++ b/kernel/sched/fair.c
>> @@ -6087,10 +6087,11 @@ static int select_idle_core(struct task_struct *p, struct sched_domain *sd, int
>>                                 break;
>>                         }
>>                 }
>> -               cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
>>
>>                 if (idle)
>>                         return core;
>> +
>> +               cpumask_andnot(cpus, cpus, cpu_smt_mask(core));
>>         }
>>
>>         /*