linux-kernel - Re: [PATCH v9 1/3] sched: Add prev_sum_exec_runtime support for RT, DL and SCX classes

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Message-ID: <08b48d52-fb1e-4d8f-8586-06280a798331@efficios.com>
Date: Mon, 24 Feb 2025 15:39:22 -0500
From: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To: Gabriele Monaco <gmonaco@...hat.com>, linux-kernel@...r.kernel.org,
 Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>
Cc: Ingo Molnar <mingo@...hat.org>, "Paul E. McKenney" <paulmck@...nel.org>,
 Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH v9 1/3] sched: Add prev_sum_exec_runtime support for RT,
 DL and SCX classes

On 2025-02-24 08:28, Gabriele Monaco wrote:
> The fair scheduling class relies on prev_sum_exec_runtime to compute the
> duration of the task's runtime since it was last scheduled. This value
> is currently not required by other scheduling classes but can be useful
> to understand long running tasks and take certain actions (e.g. during a
> scheduler tick).
> 
> Add support for prev_sum_exec_runtime to the RT, deadline and sched_ext
> classes by simply assigning the sum_exec_runtime at each set_next_task.
> 
> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@...icios.com>

> Signed-off-by: Gabriele Monaco <gmonaco@...hat.com>
> ---
>   kernel/sched/deadline.c | 1 +
>   kernel/sched/ext.c      | 1 +
>   kernel/sched/rt.c       | 1 +
>   3 files changed, 3 insertions(+)
> 
> diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
> index 38e4537790af7..438b3a953d6c7 100644
> --- a/kernel/sched/deadline.c
> +++ b/kernel/sched/deadline.c
> @@ -2391,6 +2391,7 @@ static void set_next_task_dl(struct rq *rq, struct task_struct *p, bool first)
>   	p->se.exec_start = rq_clock_task(rq);
>   	if (on_dl_rq(&p->dl))
>   		update_stats_wait_end_dl(dl_rq, dl_se);
> +	p->se.prev_sum_exec_runtime = p->se.sum_exec_runtime;
>   
>   	/* You can't push away the running task */
>   	dequeue_pushable_dl_task(rq, p);
> diff --git a/kernel/sched/ext.c b/kernel/sched/ext.c
> index 5a81d9a1e31f2..feaed0459eb92 100644
> --- a/kernel/sched/ext.c
> +++ b/kernel/sched/ext.c
> @@ -2974,6 +2974,7 @@ static void set_next_task_scx(struct rq *rq, struct task_struct *p, bool first)
>   	}
>   
>   	p->se.exec_start = rq_clock_task(rq);
> +	p->se.prev_sum_exec_runtime = p->se.sum_exec_runtime;
>   
>   	/* see dequeue_task_scx() on why we skip when !QUEUED */
>   	if (SCX_HAS_OP(running) && (p->scx.flags & SCX_TASK_QUEUED))
> diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
> index 4b8e33c615b12..1ea272e4dae71 100644
> --- a/kernel/sched/rt.c
> +++ b/kernel/sched/rt.c
> @@ -1684,6 +1684,7 @@ static inline void set_next_task_rt(struct rq *rq, struct task_struct *p, bool f
>   	p->se.exec_start = rq_clock_task(rq);
>   	if (on_rt_rq(&p->rt))
>   		update_stats_wait_end_rt(rt_rq, rt_se);
> +	p->se.prev_sum_exec_runtime = p->se.sum_exec_runtime;
>   
>   	/* The running task is never eligible for pushing */
>   	dequeue_pushable_task(rq, p);


-- 
Mathieu Desnoyers
EfficiOS Inc.
https://www.efficios.com