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From:   "Rafael J. Wysocki" <rjw@rjwysocki.net>
To:     Linux PM <linux-pm@vger.kernel.org>
Cc:     LKML <linux-kernel@vger.kernel.org>,
        Frederic Weisbecker <frederic@kernel.org>,
        Peter Zijlstra <peterz@infradead.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        "Zhou Ti (x2019cwm)" <x2019cwm@stfx.ca>
Subject: [PATCH v1 3/5] cpuidle: teo: Adjust handling of very short idle times
Date:   Mon, 29 Mar 2021 20:19:03 +0200
Message-ID: <7219614.EvYhyI6sBW@kreacher>
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From: "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>

If the time till the next timer event is shorter than the target
residency of the first idle state (state 0), the TEO governor does
not update its metrics for any idle states, but arguably it should
record a "hit" for idle state 0 in that case, so modify it to do
that.

Accordingly, also make it record an "early hit" for idle state 0 if
the measured idle duration is less than its target residency, which
allows one branch more to be dropped from teo_update().

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/cpuidle/governors/teo.c |   32 +++++++++++++++-----------------
 1 file changed, 15 insertions(+), 17 deletions(-)

Index: linux-pm/drivers/cpuidle/governors/teo.c
===================================================================
--- linux-pm.orig/drivers/cpuidle/governors/teo.c
+++ linux-pm/drivers/cpuidle/governors/teo.c
@@ -117,7 +117,8 @@ static DEFINE_PER_CPU(struct teo_cpu, te
 static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 {
 	struct teo_cpu *cpu_data = per_cpu_ptr(&teo_cpus, dev->cpu);
-	int i, idx_hit = -1, idx_timer = -1;
+	int i, idx_hit = 0, idx_timer = 0;
+	unsigned int hits, misses;
 	u64 measured_ns;
 
 	if (cpu_data->time_span_ns >= cpu_data->sleep_length_ns) {
@@ -174,25 +175,22 @@ static void teo_update(struct cpuidle_dr
 	 * also increase the "early hits" metric for the state that actually
 	 * matches the measured idle duration.
 	 */
-	if (idx_timer >= 0) {
-		unsigned int hits = cpu_data->states[idx_timer].hits;
-		unsigned int misses = cpu_data->states[idx_timer].misses;
-
-		hits -= hits >> DECAY_SHIFT;
-		misses -= misses >> DECAY_SHIFT;
-
-		if (idx_timer > idx_hit) {
-			misses += PULSE;
-			if (idx_hit >= 0)
-				cpu_data->states[idx_hit].early_hits += PULSE;
-		} else {
-			hits += PULSE;
-		}
+	hits = cpu_data->states[idx_timer].hits;
+	hits -= hits >> DECAY_SHIFT;
+
+	misses = cpu_data->states[idx_timer].misses;
+	misses -= misses >> DECAY_SHIFT;
 
-		cpu_data->states[idx_timer].misses = misses;
-		cpu_data->states[idx_timer].hits = hits;
+	if (idx_timer == idx_hit) {
+		hits += PULSE;
+	} else {
+		misses += PULSE;
+		cpu_data->states[idx_hit].early_hits += PULSE;
 	}
 
+	cpu_data->states[idx_timer].misses = misses;
+	cpu_data->states[idx_timer].hits = hits;
+
 	/*
 	 * Save idle duration values corresponding to non-timer wakeups for
 	 * pattern detection.