From 29dcbea92460e82181774b46f08b55a917615a97 Mon Sep 17 00:00:00 2001
From: Christian Loehle <christian.loehle@arm.com>
Date: Thu, 17 Oct 2024 23:00:33 +0100
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@arm.com>
Link: https://patch.msgid.link/46853b6e-bad5-4ace-9b23-ff157f234ae3@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.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 fe1be4ad88cb2..a21369eba034d 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
--
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