linux-kernel - [RFC][PATCH 3/3] cpuidle,teo: Improve state selection

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Message-ID: <20230728145808.970594909@infradead.org>
Date:   Fri, 28 Jul 2023 16:55:18 +0200
From:   Peter Zijlstra <peterz@...radead.org>
To:     anna-maria@...utronix.de, rafael@...nel.org, tglx@...utronix.de,
        frederic@...nel.org, gautham.shenoy@....com
Cc:     linux-kernel@...r.kernel.org, peterz@...radead.org,
        daniel.lezcano@...aro.org, linux-pm@...r.kernel.org,
        mingo@...hat.com, juri.lelli@...hat.com,
        vincent.guittot@...aro.org, dietmar.eggemann@....com,
        rostedt@...dmis.org, bsegall@...gle.com, mgorman@...e.de,
        bristot@...hat.com, vschneid@...hat.com
Subject: [RFC][PATCH 3/3] cpuidle,teo: Improve state selection

When selecting a state, stop when history tells us 66% of recent idles
were at or below our current state.

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
---
 drivers/cpuidle/governors/teo.c |    6 ++++++
 1 file changed, 6 insertions(+)

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -363,6 +363,7 @@ static int teo_select(struct cpuidle_dri
 	unsigned int idx_hit_sum = 0;
 	unsigned int hit_sum = 0;
 	unsigned int tick_sum = 0;
+	unsigned int thresh_sum = 0;
 	int constraint_idx = 0;
 	int idx0 = 0, idx = -1;
 	bool alt_intercepts, alt_recent;
@@ -397,6 +398,8 @@ static int teo_select(struct cpuidle_dri
 		duration_ns = tick_nohz_get_sleep_length(&delta_tick);
 	cpu_data->sleep_length_ns = duration_ns;
 
+	thresh_sum = 2 * cpu_data->total / 3; /* 66% */
+
 	/*
 	 * Find the deepest idle state whose target residency does not exceed
 	 * the current sleep length and the deepest idle state not deeper than
@@ -427,6 +430,9 @@ static int teo_select(struct cpuidle_dri
 		if (s->target_residency_ns > duration_ns)
 			break;
 
+		if (intercept_sum + hit_sum > thresh_sum)
+			break;
+
 		idx = i;
 
 		if (s->exit_latency_ns <= latency_req)