linux-kernel - Re: [PATCH 3/6] sched: Simplify sched_info

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Message-ID: <YJu8s0f7Cc78GEWN@hirez.programming.kicks-ass.net>
Date:   Wed, 12 May 2021 13:32:03 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     Mel Gorman <mgorman@...e.de>
Cc:     tglx@...utronix.de, mingo@...nel.org, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, bristot@...hat.com,
        bsingharora@...il.com, pbonzini@...hat.com, maz@...nel.org,
        linux-kernel@...r.kernel.org, kvm@...r.kernel.org,
        riel@...riel.com, hannes@...xchg.org
Subject: Re: [PATCH 3/6] sched: Simplify sched_info_on()

On Wed, May 12, 2021 at 12:10:40PM +0100, Mel Gorman wrote:
> As delta is !0 iff t->sched_info.last_queued, why not this?
> 
> diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
> index 33ffd41935ba..37e33c0eeb7c 100644
> --- a/kernel/sched/stats.h
> +++ b/kernel/sched/stats.h
> @@ -158,15 +158,14 @@ static inline void psi_sched_switch(struct task_struct *prev,
>   */
>  static inline void sched_info_dequeue(struct rq *rq, struct task_struct *t)
>  {
> -	unsigned long long delta = 0;
> -
>  	if (t->sched_info.last_queued) {
> +		unsigned long long delta;
> +
>  		delta = rq_clock(rq) - t->sched_info.last_queued;
>  		t->sched_info.last_queued = 0;
> +		t->sched_info.run_delay += delta;
> +		rq_sched_info_dequeue(rq, delta);
>  	}
> -	t->sched_info.run_delay += delta;
> -
> -	rq_sched_info_dequeue(rq, delta);
>  }

Right.. clearly I missed the obvious there.. Lemme go add another patch
on top of the lot.

Something like this I suppose.

---
diff --git a/kernel/sched/stats.h b/kernel/sched/stats.h
index 33ffd41935ba..111072ee9663 100644
--- a/kernel/sched/stats.h
+++ b/kernel/sched/stats.h
@@ -160,10 +160,11 @@ static inline void sched_info_dequeue(struct rq *rq, struct task_struct *t)
 {
 	unsigned long long delta = 0;
 
-	if (t->sched_info.last_queued) {
-		delta = rq_clock(rq) - t->sched_info.last_queued;
-		t->sched_info.last_queued = 0;
-	}
+	if (!t->sched_info.last_queued)
+		return;
+
+	delta = rq_clock(rq) - t->sched_info.last_queued;
+	t->sched_info.last_queued = 0;
 	t->sched_info.run_delay += delta;
 
 	rq_sched_info_dequeue(rq, delta);
@@ -176,12 +177,14 @@ static inline void sched_info_dequeue(struct rq *rq, struct task_struct *t)
  */
 static void sched_info_arrive(struct rq *rq, struct task_struct *t)
 {
-	unsigned long long now = rq_clock(rq), delta = 0;
+	unsigned long long now, delta = 0;
 
-	if (t->sched_info.last_queued) {
-		delta = now - t->sched_info.last_queued;
-		t->sched_info.last_queued = 0;
-	}
+	if (!t->sched_info.last_queued)
+		return;
+
+	now = rq_clock(rq);
+	delta = now - t->sched_info.last_queued;
+	t->sched_info.last_queued = 0;
 	t->sched_info.run_delay += delta;
 	t->sched_info.last_arrival = now;
 	t->sched_info.pcount++;