linux-kernel - [PATCH 01/10] clockevents: Improve clockevents_notify

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Message-ID: <20241029125451.54574-2-frederic@kernel.org>
Date: Tue, 29 Oct 2024 13:54:42 +0100
From: Frederic Weisbecker <frederic@...nel.org>
To: LKML <linux-kernel@...r.kernel.org>
Cc: Frederic Weisbecker <frederic@...nel.org>,
	Daniel Lezcano <daniel.lezcano@...aro.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Anna-Maria Behnsen <anna-maria@...utronix.de>
Subject: [PATCH 01/10] clockevents: Improve clockevents_notify_released() comment

When a new clockevent device is added and replaces a previous device,
the latter is put into the released list. Then the released list is
added back.

This may look counter-intuitive but the reason is that released device
might be suitable for other uses. For example a released CPU regular
clockevent can be a better replacement for the current broadcast event.
Similarly a released broadcast clockevent can be a better replacement
for the current regular clockevent of a given CPU.

Improve comments stating about these subtleties.

Signed-off-by: Frederic Weisbecker <frederic@...nel.org>
---
 kernel/time/clockevents.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/kernel/time/clockevents.c b/kernel/time/clockevents.c
index 78c7bd64d0dd..4af27994db93 100644
--- a/kernel/time/clockevents.c
+++ b/kernel/time/clockevents.c
@@ -337,13 +337,21 @@ int clockevents_program_event(struct clock_event_device *dev, ktime_t expires,
 }
 
 /*
- * Called after a notify add to make devices available which were
- * released from the notifier call.
+ * Called after a clockevent has been added which might
+ * have replaced a current regular or broadcast device. A
+ * released normal device might be a suitable replacement
+ * for the current broadcast device. Similarly a released
+ * broadcast device might be a suitable replacement for a
+ * normal device.
  */
 static void clockevents_notify_released(void)
 {
 	struct clock_event_device *dev;
 
+	/*
+	 * Keep iterating as long as tick_check_new_device()
+	 * replaces a device.
+	 */
 	while (!list_empty(&clockevents_released)) {
 		dev = list_entry(clockevents_released.next,
 				 struct clock_event_device, list);
-- 
2.46.0