linux-kernel - [PATCH] cpufreq: docs: Reflect latency changes in docs

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Message-ID: <46853b6e-bad5-4ace-9b23-ff157f234ae3@arm.com>
Date: Thu, 17 Oct 2024 23:00:33 +0100
From: Christian Loehle <christian.loehle@....com>
To: "Rafael J. Wysocki" <rafael@...nel.org>
Cc: Qais Yousef <qyousef@...alina.io>, Viresh Kumar
 <viresh.kumar@...aro.org>,
 "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
 linux-pm <linux-pm@...r.kernel.org>, "corbet@....net" <corbet@....net>
Subject: [PATCH] cpufreq: docs: Reflect latency changes in docs

There were two changes related to transition latency recently.
Namely commit e13aa799c2a6 ("cpufreq: Change default transition delay
to 2ms") and
commit 37c6dccd6837 ("cpufreq: Remove LATENCY_MULTIPLIER").

Both changed the defaults / maximums so let the documentation
reflect that.

Signed-off-by: Christian Loehle <christian.loehle@....com>
---
 Documentation/admin-guide/pm/cpufreq.rst | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst
index fe1be4ad88cb..a21369eba034 100644
--- a/Documentation/admin-guide/pm/cpufreq.rst
+++ b/Documentation/admin-guide/pm/cpufreq.rst
@@ -425,8 +425,8 @@ This governor exposes only one tunable:
 
 ``rate_limit_us``
 	Minimum time (in microseconds) that has to pass between two consecutive
-	runs of governor computations (default: 1000 times the scaling driver's
-	transition latency).
+	runs of governor computations (default: 1.5 times the scaling driver's
+	transition latency or the maximum 2ms).
 
 	The purpose of this tunable is to reduce the scheduler context overhead
 	of the governor which might be excessive without it.
@@ -474,17 +474,17 @@ This governor exposes the following tunables:
 	This is how often the governor's worker routine should run, in
 	microseconds.
 
-	Typically, it is set to values of the order of 10000 (10 ms).  Its
-	default value is equal to the value of ``cpuinfo_transition_latency``
-	for each policy this governor is attached to (but since the unit here
-	is greater by 1000, this means that the time represented by
-	``sampling_rate`` is 1000 times greater than the transition latency by
-	default).
+	Typically, it is set to values of the order of 2000 (2 ms).  Its
+	default value is to add a 50% breathing room
+	to ``cpuinfo_transition_latency`` on each policy this governor is
+	attached to. The minimum is typically the length of two scheduler
+	ticks.
 
 	If this tunable is per-policy, the following shell command sets the time
-	represented by it to be 750 times as high as the transition latency::
+	represented by it to be 1.5 times as high as the transition latency
+	(the default)::
 
-	# echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate
+	# echo `$(($(cat cpuinfo_transition_latency) * 3 / 2)) > ondemand/sampling_rate
 
 ``up_threshold``
 	If the estimated CPU load is above this value (in percent), the governor
-- 
2.34.1