linux-kernel - [PATCH v1 2/5] cpuidle: governors: teo: Avoid fake intercepts produced by tick

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <3404606.44csPzL39Z@rafael.j.wysocki>
Date: Wed, 14 Jan 2026 20:44:53 +0100
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Linux PM <linux-pm@...r.kernel.org>
Cc: LKML <linux-kernel@...r.kernel.org>,
 Christian Loehle <christian.loehle@....com>,
 Doug Smythies <dsmythies@...us.net>
Subject:
 [PATCH v1 2/5] cpuidle: governors: teo: Avoid fake intercepts produced by
 tick

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

Tick wakeups can lead to fake intercepts that may skew idle state
selection towards shallow states, so it is better to avoid counting
them as intercepts.

For this purpose, add a check causing teo_update() to only count
tick wakeups as intercepts if intercepts within the tick period
range are at least twice as frequent as any other events.

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

--- a/drivers/cpuidle/governors/teo.c
+++ b/drivers/cpuidle/governors/teo.c
@@ -239,6 +239,17 @@ static void teo_update(struct cpuidle_dr
 			cpu_data->state_bins[drv->state_count-1].hits += PULSE;
 			return;
 		}
+		/*
+		 * If intercepts within the tick period range are not frequent
+		 * enough, count this wakeup as a hit, since it is likely that
+		 * the tick has woken up the CPU because an expected intercept
+		 * was not there.  Otherwise, one of the intercepts may have
+		 * been incidentally preceded by the tick wakeup.
+		 */
+		if (3 * cpu_data->tick_intercepts < 2 * total) {
+			cpu_data->state_bins[idx_timer].hits += PULSE;
+			return;
+		}
 	}

 	/*