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Subject: Re: [RFC 3/3] Allow sched_{get,set}attr to change latency_tolerance
 of the task
From:   Dietmar Eggemann <dietmar.eggemann@arm.com>
To:     Parth Shah <parth@linux.ibm.com>, Qais Yousef <qais.yousef@arm.com>
Cc:     linux-kernel@vger.kernel.org, peterz@infradead.org,
        mingo@redhat.com, vincent.guittot@linaro.org,
        patrick.bellasi@matbug.net, valentin.schneider@arm.com,
        pavel@ucw.cz, dhaval.giani@oracle.com, qperret@qperret.net,
        David.Laight@ACULAB.COM, morten.rasmussen@arm.com, pjt@google.com,
        tj@kernel.org, viresh.kumar@linaro.org, rafael.j.wysocki@intel.com,
        daniel.lezcano@linaro.org
References: <20191125094618.30298-1-parth@linux.ibm.com>
 <20191125094618.30298-4-parth@linux.ibm.com>
 <20191203083915.yahl2qd3wnnkqxxs@e107158-lin.cambridge.arm.com>
 <cfb607c1-6be9-853d-cfad-6787f78fa6ad@linux.ibm.com>
 <ffe4f4de-d433-91be-00ce-20b625807f20@arm.com>
Message-ID: <09e9a3e1-9c43-a541-01e6-e1b429a63a6f@arm.com>
Date:   Fri, 6 Dec 2019 17:04:56 +0100
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On 05.12.19 10:24, Dietmar Eggemann wrote:
> On 03/12/2019 16:51, Parth Shah wrote:
>>  
>> On 12/3/19 2:09 PM, Qais Yousef wrote:
>>> On 11/25/19 15:16, Parth Shah wrote:
> 
> [...]
> 
>>>> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
>>>> index ea7abbf5c1bb..dfd36ec14404 100644
>>>> --- a/kernel/sched/core.c
>>>> +++ b/kernel/sched/core.c
>>>> @@ -4695,6 +4695,9 @@ static void __setscheduler_params(struct task_struct *p,
>>>>  	p->rt_priority = attr->sched_priority;
>>>>  	p->normal_prio = normal_prio(p);
>>>>  	set_load_weight(p, true);
>>>> +
>>>> +	/* Change latency tolerance of the task if !SCHED_FLAG_KEEP_PARAMS */
> 
> IMHO, this comment seems to be gratuitous.
> 
>>>> +	p->latency_tolerance = attr->sched_latency_tolerance;
>>>>  }
> 
> [...]
> 

This also would require some changes to UAPI
(include/uapi/linux/sched.h, include/uapi/linux/sched/types.h), see
commit a509a7cd7974 ("sched/uclamp: Extend sched_setattr() to support
utilization clamping") and tools headers UAPI
(tools/include/uapi/linux/sched.h), see commit c093de6bd3c5 ("tools
headers UAPI: Sync sched.h with the kernel").