linux-kernel - Re: [PATCH 2/2] Documentation: sched/deadline: Update GRUB description

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Date:   Wed, 10 May 2023 15:05:01 +0700
From:   Bagas Sanjaya <bagasdotme@...il.com>
To:     Vineeth Pillai <vineeth@...byteword.org>,
        luca.abeni@...tannapisa.it, Juri Lelli <juri.lelli@...hat.com>,
        Daniel Bristot de Oliveira <bristot@...hat.com>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        Steven Rostedt <rostedt@...dmis.org>,
        Joel Fernandes <joel@...lfernandes.org>,
        Dietmar Eggemann <dietmar.eggemann@....com>,
        Ben Segall <bsegall@...gle.com>, Mel Gorman <mgorman@...e.de>,
        Valentin Schneider <vschneid@...hat.com>
Cc:     Jonathan Corbet <corbet@....net>, linux-kernel@...r.kernel.org,
        linux-doc@...r.kernel.org
Subject: Re: [PATCH 2/2] Documentation: sched/deadline: Update GRUB
 description

On 5/8/23 23:08, Vineeth Pillai wrote:
> diff --git a/Documentation/scheduler/sched-deadline.rst b/Documentation/scheduler/sched-deadline.rst
> index 9d9be52f221a..0c73f07f712d 100644
> --- a/Documentation/scheduler/sched-deadline.rst
> +++ b/Documentation/scheduler/sched-deadline.rst
> @@ -195,11 +195,15 @@ Deadline Task Scheduling
>        its utilization is added to the active utilization of the runqueue where
>        it has been enqueued.
>  
> - For each runqueue, the algorithm GRUB keeps track of two different bandwidths:
> + For each runqueue, the algorithm GRUB keeps track of three different bandwidths:
>  
>    - Active bandwidth (running_bw): this is the sum of the bandwidths of all
>      tasks in active state (i.e., ActiveContending or ActiveNonContending);
>  
> +  - Active bandwidth of SCHED_FLAG_RECLAIM tasks(reclaim_bw): this is the sum of
> +    bandwidth of all tasks in active state which participates in GRUB. This is a
> +    subset of running_bw and is needed for reclaimable bandwidth calculation.
> +
>    - Total bandwidth (this_bw): this is the sum of all tasks "belonging" to the
>      runqueue, including the tasks in Inactive state.
>  
> @@ -209,12 +213,12 @@ Deadline Task Scheduling
>   to
>  
>             dq = -max{ Ui / Umax, (1 - Uinact - Uextra) } dt
> +           dq = -(Ureclaim / (Uextra + Uinact + Ureclaim)) dt
>  
>   where:
>  
> -  - Ui is the bandwidth of task Ti;
> -  - Umax is the maximum reclaimable utilization (subjected to RT throttling
> -    limits);
> +  - Ureclaim is the (per runqueue) bandwidth of all SCHED_FLAG_RECLAIM tasks
> +    in active state;
>    - Uinact is the (per runqueue) inactive utilization, computed as
>      (this_bq - running_bw);
>    - Uextra is the (per runqueue) extra reclaimable utilization
> @@ -222,7 +226,8 @@ Deadline Task Scheduling
>  
>  
>   Let's now see a trivial example of two deadline tasks with runtime equal
> - to 4 and period equal to 8 (i.e., bandwidth equal to 0.5)::
> + to 4 and period equal to 8 (i.e., bandwidth equal to 0.5). Tasks are
> + allowed to use the whole cpu(Umax = 1)::
>  
>           A            Task T1
>           |
> @@ -244,7 +249,7 @@ Deadline Task Scheduling
>           0   1   2   3   4   5   6   7   8
>  
>  
> -         A            running_bw
> +         A            reclaim_bw
>           |
>         1 -----------------               ------
>           |               |               |
> @@ -272,7 +277,7 @@ Deadline Task Scheduling
>  
>      This is the 0-lag time for Task T1. Since it didn't woken up in the
>      meantime, it enters the Inactive state. Its bandwidth is removed from
> -    running_bw.
> +    running_bw and reclaim_bw.
>      Task T2 continues its execution. However, its runtime is now decreased as
>      dq = - 0.5 dt because Uinact = 0.5.
>      Task T2 therefore reclaims the bandwidth unused by Task T1.
> @@ -280,7 +285,7 @@ Deadline Task Scheduling
>    - Time t = 8:
>  
>      Task T1 wakes up. It enters the ActiveContending state again, and the
> -    running_bw is incremented.
> +    running_bw and reclaim_bw are incremented.
>  
>  
>  2.3 Energy-aware scheduling

LGTM, thanks!

Reviewed-by: Bagas Sanjaya <bagasdotme@...il.com>

-- 
An old man doll... just what I always wanted! - Clara