linux-kernel - [PATCH v1 0/2] cpuidle: teo: Refine handling of short idle intervals

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Message-ID: <4661520.LvFx2qVVIh@rjwysocki.net>
Date: Thu, 03 Apr 2025 21:16:08 +0200
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>,
 Doug Smythies <dsmythies@...us.net>,
 Aboorva Devarajan <aboorvad@...ux.ibm.com>
Subject: [PATCH v1 0/2] cpuidle: teo: Refine handling of short idle intervals

Hi Everyone,

This series is intended to address an issue with overly aggressive selection
of idle state 0 (the polling state) in teo on x86 in some cases when timer
wakeups dominate the CPU wakeup pattern.

In those cases, timer wakeups are not taken into account when they are
within the LATENCY_THRESHOLD_NS range and the idle state selection may
be based entirely on non-timer wakeups which may be rare.  This causes
the prediction accuracy to be low and too much energy may be used as
a result.

The first patch is preparatory and it is not expected to make any
functional difference.

The second patch causes teo to take timer wakeups into account if it
is about to skip the tick_nohz_get_sleep_length() invocation, so they
get a chance to influence the idle state selection.

I have been using this series on my systems for several weeks and observed
a significant reduction of the polling state selection rate in multiple
workloads.

Thanks!