linux-kernel - [PATCH 3/8] sched/eevdf: Fix HRTICK duration

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Message-ID: <20250918080205.716937764@infradead.org>
Date: Thu, 18 Sep 2025 09:52:22 +0200
From: Peter Zijlstra <peterz@...radead.org>
To: tglx@...utronix.de
Cc: arnd@...db.de,
 anna-maria@...utronix.de,
 frederic@...nel.org,
 peterz@...radead.org,
 luto@...nel.org,
 mingo@...hat.com,
 juri.lelli@...hat.com,
 vincent.guittot@...aro.org,
 dietmar.eggemann@....com,
 rostedt@...dmis.org,
 bsegall@...gle.com,
 mgorman@...e.de,
 vschneid@...hat.com,
 linux-kernel@...r.kernel.org,
 oliver.sang@...el.com
Subject: [PATCH 3/8] sched/eevdf: Fix HRTICK duration

The nominal duration for an EEVDF task to run is until its deadline.
At which point the deadline is moved ahead and a new task selection is
done.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c |   40 +++++++++++++++++++++++++++++-----------
 1 file changed, 29 insertions(+), 11 deletions(-)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -6775,21 +6775,39 @@ static inline void sched_fair_update_sto
 static void hrtick_start_fair(struct rq *rq, struct task_struct *p)
 {
 	struct sched_entity *se = &p->se;
+	unsigned long scale = 1024;
+	unsigned long util = 0;
+	u64 vdelta;
+	u64 delta;
 
 	WARN_ON_ONCE(task_rq(p) != rq);
 
-	if (rq->cfs.h_nr_queued > 1) {
-		u64 ran = se->sum_exec_runtime - se->prev_sum_exec_runtime;
-		u64 slice = se->slice;
-		s64 delta = slice - ran;
-
-		if (delta < 0) {
-			if (task_current_donor(rq, p))
-				resched_curr(rq);
-			return;
-		}
-		hrtick_start(rq, delta);
+	if (rq->cfs.h_nr_queued <= 1)
+		return;
+
+	/*
+	 * Compute time until virtual deadline
+	 */
+	vdelta = se->deadline - se->vruntime;
+	if ((s64)vdelta < 0) {
+		if (task_current_donor(rq, p))
+			resched_curr(rq);
+		return;
+	}
+	delta = (se->load.weight * vdelta) / NICE_0_LOAD;
+
+	/*
+	 * Correct for instantaneous load of other classes.
+	 */
+	util += cpu_util_dl(rq);
+	util += cpu_util_rt(rq);
+	util += cpu_util_irq(rq);
+	if (util && util < 1024) {
+		scale *= 1024;
+		scale /= (1024 - util);
 	}
+
+	hrtick_start(rq, (scale * delta) / 1024);
 }
 
 /*