linux-kernel - [tip: timers/core] clockevents: Improve clockevents_notify

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Message-ID: <173031921690.3137.8686198378080958241.tip-bot2@tip-bot2>
Date: Wed, 30 Oct 2024 20:13:36 -0000
From: "tip-bot2 for Frederic Weisbecker" <tip-bot2@...utronix.de>
To: linux-tip-commits@...r.kernel.org
Cc: Frederic Weisbecker <frederic@...nel.org>,
 Thomas Gleixner <tglx@...utronix.de>, x86@...nel.org,
 linux-kernel@...r.kernel.org
Subject:
 [tip: timers/core] clockevents: Improve clockevents_notify_released() comment

The following commit has been merged into the timers/core branch of tip:

Commit-ID:     679f8484cafa08f49a19e2947d05e96321fbed9d
Gitweb:        https://git.kernel.org/tip/679f8484cafa08f49a19e2947d05e96321fbed9d
Author:        Frederic Weisbecker <frederic@...nel.org>
AuthorDate:    Tue, 29 Oct 2024 13:54:42 +01:00
Committer:     Thomas Gleixner <tglx@...utronix.de>
CommitterDate: Wed, 30 Oct 2024 21:02:21 +01:00

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>
Signed-off-by: Thomas Gleixner <tglx@...utronix.de>
Link: https://lore.kernel.org/all/20241029125451.54574-2-frederic@kernel.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 78c7bd6..4af2799 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);