Received-SPF: pass (google.com: domain of linux-kernel+bounces-183268-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Message-ID: <0ce2d536-1125-4df8-9a5b-0d5e389cd8af@arm.com>
Date: Sun, 19 May 2024 22:03:59 +0100
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Content-Language: en-US
To: "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
 linux-pm@vger.kernel.org, "Rafael J. Wysocki" <rafael@kernel.org>,
 Daniel Lezcano <daniel.lezcano@linaro.org>
Cc: Qais Yousef <qyousef@layalina.io>, kajetan.puchalski@arm.com,
 Anna-Maria Behnsen <anna-maria@linutronix.de>
From: Christian Loehle <christian.loehle@arm.com>
Subject: [PATCH] cpuidle: teo: fix underflow of recent intercepts
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 7bit

The recent counter of each cpuidle state bin reflects the number of
recent intercepts. It's decremented and incremented accordingly.
The decrement was never checked for 0, therefore underflowing into a
value teo cannot easily recover from.

The underflow lead to deeper idle states being skipped because teo
assumed interception was likely and it preferring shallower states.

Fixes: 77577558f25d ("cpuidle: teo: Rework most recent idle duration values treatment")
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
---
 drivers/cpuidle/governors/teo.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c
index 7244f71c59c5..42fb2771e35d 100644
--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -290,7 +290,8 @@ static void teo_update(struct cpuidle_driver *drv, struct cpuidle_device *dev)
 	if (cpu_data->next_recent_idx >= NR_RECENT)
 		cpu_data->next_recent_idx = 0;
 
-	if (cpu_data->recent_idx[i] >= 0)
+	if (cpu_data->recent_idx[i] >= 0 &&
+			cpu_data->state_bins[cpu_data->recent_idx[i]].recent)
 		cpu_data->state_bins[cpu_data->recent_idx[i]].recent--;
 
 	/*
-- 
2.34.1