linux-kernel - [PATCH 4/8] hrtimer: Optimize __hrtimer_start_range

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Message-ID: <20250918080205.835307230@infradead.org>
Date: Thu, 18 Sep 2025 09:52:23 +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 4/8] hrtimer: Optimize __hrtimer_start_range_ns()

Much like hrtimer_reprogram(), skip programming is the cpu_base is
running the hrtimer interrupt.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 kernel/time/hrtimer.c |    8 ++++++++
 1 file changed, 8 insertions(+)

--- a/kernel/time/hrtimer.c
+++ b/kernel/time/hrtimer.c
@@ -1261,6 +1261,14 @@ static int __hrtimer_start_range_ns(stru
 	}
 
 	first = enqueue_hrtimer(timer, new_base, mode);
+
+	/*
+	 * If the hrtimer interrupt is running, then it will reevaluate the
+	 * clock bases and reprogram the clock event device.
+	 */
+	if (new_base->cpu_base->in_hrtirq)
+		return 0;
+
 	if (!force_local) {
 		/*
 		 * If the current CPU base is online, then the timer is