linux-kernel - Re: [RFC 1/3] Introduce latency-tolerance as an per-task attribute

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Message-ID: <20191203083654.3ctttimdiujdt7tl@e107158-lin.cambridge.arm.com>
Date:   Tue, 3 Dec 2019 08:36:54 +0000
From:   Qais Yousef <qais.yousef@....com>
To:     Parth Shah <parth@...ux.ibm.com>
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        mingo@...hat.com, vincent.guittot@...aro.org,
        patrick.bellasi@...bug.net, valentin.schneider@....com,
        pavel@....cz, dhaval.giani@...cle.com, qperret@...rret.net,
        David.Laight@...LAB.COM, morten.rasmussen@....com, pjt@...gle.com,
        tj@...nel.org, dietmar.eggemann@....com, viresh.kumar@...aro.org,
        rafael.j.wysocki@...el.com, daniel.lezcano@...aro.org
Subject: Re: [RFC 1/3] Introduce latency-tolerance as an per-task attribute

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@...ux.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 :)

--
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
>