linux-kernel - [PATCH 2/8] sched/fair: Limit hrtick work

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Message-ID: <20250918080205.563385766@infradead.org>
Date: Thu, 18 Sep 2025 09:52:21 +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 2/8] sched/fair: Limit hrtick work

The task_tick_fair() function does:

 - update the hierarchical runtimes
 - drive numa-balancing
 - update load-balance statistics
 - drive force-idle preemption

All but the very first can be limited to the periodic tick. Let hrtick
only update accounting and drive preemption, not load-balancing and
other bits.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/sched/fair.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -13119,6 +13119,12 @@ static void task_tick_fair(struct rq *rq
 		entity_tick(cfs_rq, se, queued);
 	}
 
+	if (queued) {
+		if (!need_resched())
+			hrtick_start_fair(rq, curr);
+		return;
+	}
+
 	if (static_branch_unlikely(&sched_numa_balancing))
 		task_tick_numa(rq, curr);