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@efficios.com>
Signed-off-by: Gabriele Monaco <gmonaco@redhat.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);
-- 
2.48.1

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@efficios.com>

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

> Signed-off-by: Gabriele Monaco <gmonaco@redhat.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