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Subject: Re: [RFC 1/3] Introduce latency-tolerance as an per-task attribute
To:     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, dietmar.eggemann@arm.com, viresh.kumar@linaro.org,
        rafael.j.wysocki@intel.com, daniel.lezcano@linaro.org
References: <20191125094618.30298-1-parth@linux.ibm.com>
 <20191125094618.30298-2-parth@linux.ibm.com>
 <20191203083654.3ctttimdiujdt7tl@e107158-lin.cambridge.arm.com>
From:   Parth Shah <parth@linux.ibm.com>
Date:   Tue, 3 Dec 2019 21:17:11 +0530
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On 12/3/19 2:06 PM, Qais Yousef wrote:
> On 11/25/19 15:16, Parth Shah wrote:
>> Latency-tolerance indicates the latency requirements of a task with respect
>> to the other tasks in the system. The value of the attribute can be within
>> the range of [-20, 19] both inclusive to be in-line with the values just
>> like task nice values.
>>
>> latency_tolerance = -20 indicates the task to have the least latency as
>> compared to the tasks having latency_tolerance = +19.
>>
>> The latency_tolerance may affect only the CFS SCHED_CLASS by getting
>> latency requirements from the userspace.
>>
>> Signed-off-by: Parth Shah <parth@linux.ibm.com>
>> ---
>>  include/linux/sched.h                   |  3 +++
>>  include/linux/sched/latency_tolerance.h | 13 +++++++++++++
>>  2 files changed, 16 insertions(+)
>>  create mode 100644 include/linux/sched/latency_tolerance.h
>>
>> diff --git a/include/linux/sched.h b/include/linux/sched.h
>> index 2c2e56bd8913..bcc1c1d0856d 100644
>> --- a/include/linux/sched.h
>> +++ b/include/linux/sched.h
>> @@ -25,6 +25,7 @@
>>  #include <linux/resource.h>
>>  #include <linux/latencytop.h>
>>  #include <linux/sched/prio.h>
>> +#include <linux/sched/latency_tolerance.h>
>>  #include <linux/sched/types.h>
>>  #include <linux/signal_types.h>
>>  #include <linux/mm_types_task.h>
>> @@ -666,6 +667,8 @@ struct task_struct {
>>  #endif
>>  	int				on_rq;
>>  
>> +	int				latency_tolerance;
>> +
>>  	int				prio;
>>  	int				static_prio;
>>  	int				normal_prio;
>> diff --git a/include/linux/sched/latency_tolerance.h b/include/linux/sched/latency_tolerance.h
>> new file mode 100644
>> index 000000000000..7a00abe05bc4
>> --- /dev/null
>> +++ b/include/linux/sched/latency_tolerance.h
>> @@ -0,0 +1,13 @@
>> +/* SPDX-License-Identifier: GPL-2.0 */
>> +#ifndef _LINUX_SCHED_LATENCY_TOLERANCE_H
>> +#define _LINUX_SCHED_LATENCY_TOLERANCE_H
> 
> nit: Add some description here explaining what latency tolerance is please. You
> copy paste some text from your cover letter :)

Sure. Will add some text here.

> 
> --
> Qais Youesf
> 
>> +
>> +#define MAX_LATENCY_TOLERANCE	19
>> +#define MIN_LATENCY_TOLERANCE	-20
>> +
>> +#define LATENCY_TOLERANCE_WIDTH	\
>> +	(MAX_LATENCY_TOLERANCE - MIN_LATENCY_TOLERANCE + 1)
>> +
>> +#define DEFAULT_LATENCY_TOLERANCE	0
>> +
>> +#endif /* _LINUX_SCHED_LATENCY_TOLERANCE_H */
>> -- 
>> 2.17.2
>>