From 154ae8bb3c830f0a568a5194ce7e631aa6bcfe8b Mon Sep 17 00:00:00 2001 From: "Rafael J. Wysocki" Date: Wed, 2 Jun 2021 20:18:02 +0200 Subject: cpuidle: teo: Use kerneldoc documentation in admin-guide There are two descriptions of the TEO (Timer Events Oriented) cpuidle governor in the kernel source tree, one in the C file containing its code and one in cpuidle.rst which is part of admin-guide. Instead of trying to keep them both in sync and in order to reduce text duplication, include the governor description from the C file directly into cpuidle.rst. Signed-off-by: Rafael J. Wysocki --- Documentation/admin-guide/pm/cpuidle.rst | 77 +------------------------------- drivers/cpuidle/governors/teo.c | 12 +++-- 2 files changed, 10 insertions(+), 79 deletions(-) diff --git a/Documentation/admin-guide/pm/cpuidle.rst b/Documentation/admin-guide/pm/cpuidle.rst index 10fde58d0869..aec2cd2aaea7 100644 --- a/Documentation/admin-guide/pm/cpuidle.rst +++ b/Documentation/admin-guide/pm/cpuidle.rst @@ -347,81 +347,8 @@ for tickless systems. It follows the same basic strategy as the ``menu`` `one `_: it always tries to find the deepest idle state suitable for the given conditions. However, it applies a different approach to that problem. -First, it does not use sleep length correction factors, but instead it attempts -to correlate the observed idle duration values with the available idle states -and use that information to pick up the idle state that is most likely to -"match" the upcoming CPU idle interval. Second, it does not take the tasks -that were running on the given CPU in the past and are waiting on some I/O -operations to complete now at all (there is no guarantee that they will run on -the same CPU when they become runnable again) and the pattern detection code in -it avoids taking timer wakeups into account. It also only uses idle duration -values less than the current time till the closest timer (with the scheduler -tick excluded) for that purpose. - -Like in the ``menu`` governor `case `_, the first step is to obtain -the *sleep length*, which is the time until the closest timer event with the -assumption that the scheduler tick will be stopped (that also is the upper bound -on the time until the next CPU wakeup). That value is then used to preselect an -idle state on the basis of three metrics maintained for each idle state provided -by the ``CPUIdle`` driver: ``hits``, ``misses`` and ``early_hits``. - -The ``hits`` and ``misses`` metrics measure the likelihood that a given idle -state will "match" the observed (post-wakeup) idle duration if it "matches" the -sleep length. They both are subject to decay (after a CPU wakeup) every time -the target residency of the idle state corresponding to them is less than or -equal to the sleep length and the target residency of the next idle state is -greater than the sleep length (that is, when the idle state corresponding to -them "matches" the sleep length). The ``hits`` metric is increased if the -former condition is satisfied and the target residency of the given idle state -is less than or equal to the observed idle duration and the target residency of -the next idle state is greater than the observed idle duration at the same time -(that is, it is increased when the given idle state "matches" both the sleep -length and the observed idle duration). In turn, the ``misses`` metric is -increased when the given idle state "matches" the sleep length only and the -observed idle duration is too short for its target residency. - -The ``early_hits`` metric measures the likelihood that a given idle state will -"match" the observed (post-wakeup) idle duration if it does not "match" the -sleep length. It is subject to decay on every CPU wakeup and it is increased -when the idle state corresponding to it "matches" the observed (post-wakeup) -idle duration and the target residency of the next idle state is less than or -equal to the sleep length (i.e. the idle state "matching" the sleep length is -deeper than the given one). - -The governor walks the list of idle states provided by the ``CPUIdle`` driver -and finds the last (deepest) one with the target residency less than or equal -to the sleep length. Then, the ``hits`` and ``misses`` metrics of that idle -state are compared with each other and it is preselected if the ``hits`` one is -greater (which means that that idle state is likely to "match" the observed idle -duration after CPU wakeup). If the ``misses`` one is greater, the governor -preselects the shallower idle state with the maximum ``early_hits`` metric -(or if there are multiple shallower idle states with equal ``early_hits`` -metric which also is the maximum, the shallowest of them will be preselected). -[If there is a wakeup latency constraint coming from the `PM QoS framework -`_ which is hit before reaching the deepest idle state with the -target residency within the sleep length, the deepest idle state with the exit -latency within the constraint is preselected without consulting the ``hits``, -``misses`` and ``early_hits`` metrics.] - -Next, the governor takes several idle duration values observed most recently -into consideration and if at least a half of them are greater than or equal to -the target residency of the preselected idle state, that idle state becomes the -final candidate to ask for. Otherwise, the average of the most recent idle -duration values below the target residency of the preselected idle state is -computed and the governor walks the idle states shallower than the preselected -one and finds the deepest of them with the target residency within that average. -That idle state is then taken as the final candidate to ask for. - -Still, at this point the governor may need to refine the idle state selection if -it has not decided to `stop the scheduler tick `_. That -generally happens if the target residency of the idle state selected so far is -less than the tick period and the tick has not been stopped already (in a -previous iteration of the idle loop). Then, like in the ``menu`` governor -`case `_, the sleep length used in the previous computations may not -reflect the real time until the closest timer event and if it really is greater -than that time, a shallower state with a suitable target residency may need to -be selected. - +.. kernel-doc:: drivers/cpuidle/governors/teo.c + :doc: teo-description .. _idle-states-representation: diff --git a/drivers/cpuidle/governors/teo.c b/drivers/cpuidle/governors/teo.c index 7c2024f91fd7..1e0b2f828abb 100644 --- a/drivers/cpuidle/governors/teo.c +++ b/drivers/cpuidle/governors/teo.c @@ -4,6 +4,10 @@ * * Copyright (C) 2018 - 2021 Intel Corporation * Author: Rafael J. Wysocki + */ + +/** + * DOC: teo-description * * The idea of this governor is based on the observation that on many systems * timer events are two or more orders of magnitude more frequent than any @@ -28,7 +32,7 @@ * * The computations carried out by this governor are based on using bins whose * boundaries are aligned with the target residency parameter values of the CPU - * idle states provided by the cpuidle driver in the ascending order. That is, + * idle states provided by the %CPUIdle driver in the ascending order. That is, * the first bin spans from 0 up to, but not including, the target residency of * the second idle state (idle state 1), the second bin spans from the target * residency of idle state 1 up to, but not including, the target residency of @@ -51,8 +55,8 @@ * situations are referred to as "intercepts" below). * * In addition to the metrics described above, the governor counts recent - * intercepts (that is, intercepts that have occurred during the last NR_RECENT - * invocations of it for the given CPU) for each bin. + * intercepts (that is, intercepts that have occurred during the last + * %NR_RECENT invocations of it for the given CPU) for each bin. * * In order to select an idle state for a CPU, the governor takes the following * steps (modulo the possible latency constraint that must be taken into account @@ -76,7 +80,7 @@ * shallower than the candidate one. * * 2. If the second sum is greater than the first one or the third sum is - * greater than NR_RECENT / 2, the CPU is likely to wake up early, so look + * greater than %NR_RECENT / 2, the CPU is likely to wake up early, so look * for an alternative idle state to select. * * - Traverse the idle states shallower than the candidate one in the -- cgit v1.2.3