linux-kernel - [PATCH v1 5/9] cpuidle: teo: Clarify two code comments

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Message-ID: <8472971.T7Z3S40VBb@rjwysocki.net>
Date: Mon, 13 Jan 2025 19:41:55 +0100
From: "Rafael J. Wysocki" <rjw@...ysocki.net>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Daniel Lezcano <daniel.lezcano@...aro.org>,
 Christian Loehle <christian.loehle@....com>,
 Artem Bityutskiy <artem.bityutskiy@...ux.intel.com>
Subject: [PATCH v1 5/9] cpuidle: teo: Clarify two code comments

From: Rafael J. Wysocki <rafael.j.wysocki@...el.com>

Rewrite two code comments suposed to explain its behavior that are too
concise or not sufficiently clear.

No functional impact.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
---
 drivers/cpuidle/governors/teo.c |   16 +++++++++++-----
 1 file changed, 11 insertions(+), 5 deletions(-)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -154,9 +154,10 @@
 
 	if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) {
 		/*
-		 * One of the safety nets has triggered or the wakeup was close
-		 * enough to the closest timer event expected at the idle state
-		 * selection time to be discarded.
+		 * This causes the wakeup to be counted as a hit regardless of
+		 * regardless of the real idle duration which doesn't need to be
+		 * computed because the wakeup has been close enough to an
+		 * anticipated timer.
 		 */
 		measured_ns = U64_MAX;
 	} else {
@@ -302,8 +303,13 @@
 
 	cpu_data->time_span_ns = local_clock();
 	/*
-	 * Set the expected sleep length to infinity in case of an early
-	 * return.
+	 * Set the sleep length to infitity in case the invocation of
+	 * tick_nohz_get_sleep_length() below is skipped, in which case it won't
+	 * be known whether or not the subsequent wakeup is caused by a timer.
+	 * It is generally fine to count the wakeup as an intercept then, except
+	 * for the cases when the CPU is mostly woken up by timers and there may
+	 * be opportunities to ask for a deeper idle state when no imminent
+	 * timers are scheduled which may be missed.
 	 */
 	cpu_data->sleep_length_ns = KTIME_MAX;