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Subject: Re: [RFC PATCH 3/9] sched: add sched feature to disable idle core
 search
To:     Patrick Bellasi <patrick.bellasi@arm.com>
Cc:     linux-kernel@vger.kernel.org, peterz@infradead.org,
        mingo@redhat.com, tglx@linutronix.de, steven.sistare@oracle.com,
        dhaval.giani@oracle.com, daniel.lezcano@linaro.org,
        vincent.guittot@linaro.org, viresh.kumar@linaro.org,
        tim.c.chen@linux.intel.com, mgorman@techsingularity.net,
        parth@linux.ibm.com
References: <20190830174944.21741-1-subhra.mazumdar@oracle.com>
 <20190830174944.21741-4-subhra.mazumdar@oracle.com> <87mufj2gju.fsf@arm.com>
From:   Subhra Mazumdar <subhra.mazumdar@oracle.com>
Message-ID: <031de1c0-c5a5-ea88-1e9c-836452fccf9c@oracle.com>
Date:   Thu, 5 Sep 2019 15:02:09 -0700
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On 9/5/19 3:17 AM, Patrick Bellasi wrote:
> On Fri, Aug 30, 2019 at 18:49:38 +0100, subhra mazumdar wrote...
>
>> Add a new sched feature SIS_CORE to have an option to disable idle core
>> search (select_idle_core).
>>
>> Signed-off-by: subhra mazumdar <subhra.mazumdar@oracle.com>
>> ---
>>   kernel/sched/features.h | 1 +
>>   1 file changed, 1 insertion(+)
>>
>> diff --git a/kernel/sched/features.h b/kernel/sched/features.h
>> index 858589b..de4d506 100644
>> --- a/kernel/sched/features.h
>> +++ b/kernel/sched/features.h
>> @@ -57,6 +57,7 @@ SCHED_FEAT(TTWU_QUEUE, true)
>>    */
>>   SCHED_FEAT(SIS_AVG_CPU, false)
>>   SCHED_FEAT(SIS_PROP, true)
>> +SCHED_FEAT(SIS_CORE, true)
> Why do we need a sched_feature? If you think there are systems in
> which the usage of latency-nice does not make sense for in "Select Idle
> Sibling", then we should probably better add a new Kconfig option.
This is not for latency-nice but to be able to disable a different aspect
of the scheduler, i.e searching for idle cores. This can be made part of
latency-nice (i.e not do idle core search if latency-nice is below a
certain value) but even then having a feature to disable it doesn't hurt.
>
> If that's the case, you can probably use the init/Kconfig's
> "Scheduler features" section, recently added by:
>
>    commit 69842cba9ace ("sched/uclamp: Add CPU's clamp buckets refcounting")
>
>>   /*
>>    * Issue a WARN when we do multiple update_rq_clock() calls
> Best,
> Patrick
>