[PATCH 35/57] docs: timers: convert documentation to ReST

Mauro Carvalho Chehab
2019-04-16T03:02:54Z

The conversion here is really trivial: just a bunch of title
markups and very few puntual changes is enough to make it to
be parsed by Sphinx and generate a nice html.

Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
---
Documentation/timers/NO_HZ.txt | 40 ++++++++++++++++-----------
Documentation/timers/highres.txt | 11 ++++----
Documentation/timers/hpet.txt | 4 ++-
Documentation/timers/hrtimers.txt | 6 ++--
Documentation/timers/timekeeping.txt | 3 +-
Documentation/timers/timers-howto.txt | 15 +++++++---
6 files changed, 49 insertions(+), 30 deletions(-)

diff --git a/Documentation/timers/NO_HZ.txt b/Documentation/timers/NO_HZ.txt
index 9591092da5e0..065db217cb04 100644
--- a/Documentation/timers/NO_HZ.txt
+++ b/Documentation/timers/NO_HZ.txt
@@ -1,4 +1,6 @@
- NO_HZ: Reducing Scheduling-Clock Ticks
+﻿======================================
+NO_HZ: Reducing Scheduling-Clock Ticks
+======================================

This document describes Kconfig options and boot parameters that can
@@ -28,7 +30,8 @@ by a third section on RCU-specific considerations, a fourth section
discussing testing, and a fifth and final section listing known issues.

-NEVER OMIT SCHEDULING-CLOCK TICKS
+Never Omit Scheduling-Clock Ticks
+=================================

Very old versions of Linux from the 1990s and the very early 2000s
are incapable of omitting scheduling-clock ticks. It turns out that
@@ -59,7 +62,8 @@ degrade your applications performance. If this describes your workload,
you should read the following two sections.

-OMIT SCHEDULING-CLOCK TICKS FOR IDLE CPUs
+Omit Scheduling-Clock Ticks For Idle CPUs
+=========================================

If a CPU is idle, there is little point in sending it a scheduling-clock
interrupt. After all, the primary purpose of a scheduling-clock interrupt
@@ -97,7 +101,8 @@ By default, CONFIG_NO_HZ_IDLE=y kernels boot with "nohz=on", enabling
dyntick-idle mode.

-OMIT SCHEDULING-CLOCK TICKS FOR CPUs WITH ONLY ONE RUNNABLE TASK
+Omit Scheduling-Clock Ticks For CPUs With Only One Runnable Task
+================================================================

If a CPU has only one runnable task, there is little point in sending it
a scheduling-clock interrupt because there is no other task to switch to.
@@ -174,7 +179,8 @@ However, the drawbacks listed above mean that adaptive ticks should not
(yet) be enabled by default.

-RCU IMPLICATIONS
+RCU Implications
+================

There are situations in which idle CPUs cannot be permitted to
enter either dyntick-idle mode or adaptive-tick mode, the most
@@ -199,7 +205,8 @@ scheduler will decide where to run them, which might or might not be
where you want them to run.

-TESTING
+Testing
+=======

So you enable all the OS-jitter features described in this document,
but do not see any change in your workload's behavior. Is this because
@@ -222,9 +229,10 @@ We do not currently have a good way to remove OS jitter from single-CPU
systems.

-KNOWN ISSUES
+Known Issues
+============

-o Dyntick-idle slows transitions to and from idle slightly.
+* Dyntick-idle slows transitions to and from idle slightly.
In practice, this has not been a problem except for the most
aggressive real-time workloads, which have the option of disabling
dyntick-idle mode, an option that most of them take. However,
@@ -248,13 +256,13 @@ o Dyntick-idle slows transitions to and from idle slightly.
this parameter effectively disables Turbo Mode on Intel
CPUs, which can significantly reduce maximum performance.

-o Adaptive-ticks slows user/kernel transitions slightly.
+* Adaptive-ticks slows user/kernel transitions slightly.
This is not expected to be a problem for computationally intensive
workloads, which have few such transitions. Careful benchmarking
will be required to determine whether or not other workloads
are significantly affected by this effect.

-o Adaptive-ticks does not do anything unless there is only one
+* Adaptive-ticks does not do anything unless there is only one
runnable task for a given CPU, even though there are a number
of other situations where the scheduling-clock tick is not
needed. To give but one example, consider a CPU that has one
@@ -275,7 +283,7 @@ o Adaptive-ticks does not do anything unless there is only one

Better handling of these sorts of situations is future work.

-o A reboot is required to reconfigure both adaptive idle and RCU
+* A reboot is required to reconfigure both adaptive idle and RCU
callback offloading. Runtime reconfiguration could be provided
if needed, however, due to the complexity of reconfiguring RCU at
runtime, there would need to be an earthshakingly good reason.
@@ -283,12 +291,12 @@ o A reboot is required to reconfigure both adaptive idle and RCU
simply offloading RCU callbacks from all CPUs and pinning them
where you want them whenever you want them pinned.

-o Additional configuration is required to deal with other sources
+* Additional configuration is required to deal with other sources
of OS jitter, including interrupts and system-utility tasks
and processes. This configuration normally involves binding
interrupts and tasks to particular CPUs.

-o Some sources of OS jitter can currently be eliminated only by
+* Some sources of OS jitter can currently be eliminated only by
constraining the workload. For example, the only way to eliminate
OS jitter due to global TLB shootdowns is to avoid the unmapping
operations (such as kernel module unload operations) that
@@ -299,17 +307,17 @@ o Some sources of OS jitter can currently be eliminated only by
helpful, especially when combined with the mlock() and mlockall()
system calls.

-o Unless all CPUs are idle, at least one CPU must keep the
+* Unless all CPUs are idle, at least one CPU must keep the
scheduling-clock interrupt going in order to support accurate
timekeeping.

-o If there might potentially be some adaptive-ticks CPUs, there
+* If there might potentially be some adaptive-ticks CPUs, there
will be at least one CPU keeping the scheduling-clock interrupt
going, even if all CPUs are otherwise idle.

Better handling of this situation is ongoing work.

-o Some process-handling operations still require the occasional
+* Some process-handling operations still require the occasional
scheduling-clock tick. These operations include calculating CPU
load, maintaining sched average, computing CFS entity vruntime,
computing avenrun, and carrying out load balancing. They are
diff --git a/Documentation/timers/highres.txt b/Documentation/timers/highres.txt
index 8f9741592123..f93528e6f1c8 100644
--- a/Documentation/timers/highres.txt
+++ b/Documentation/timers/highres.txt
@@ -1,5 +1,6 @@
+=====================================================
High resolution timers and dynamic ticks design notes
------------------------------------------------------
+=====================================================

Further information can be found in the paper of the OLS 2006 talk "hrtimers
and beyond". The paper is part of the OLS 2006 Proceedings Volume 1, which can
@@ -35,6 +36,7 @@ also figure #2 (OLS slides p. 15)

The main differences to the timer wheel, which holds the armed timer_list type
timers are:
+
- time ordered enqueueing into a rb-tree
- independent of ticks (the processing is based on nanoseconds)

@@ -55,7 +57,8 @@ merged into the 2.6.18 kernel.

Further information about the Generic Time Of Day framework is available in the
OLS 2005 Proceedings Volume 1:
-http://www.linuxsymposium.org/2005/linuxsymposium_procv1.pdf
+
+ http://www.linuxsymposium.org/2005/linuxsymposium_procv1.pdf

The paper "We Are Not Getting Any Younger: A New Approach to Time and
Timers" was written by J. Stultz, D.V. Hart, & N. Aravamudan.
@@ -100,6 +103,7 @@ accounting, profiling, and high resolution timers.

The management layer assigns one or more of the following functions to a clock
event device:
+
- system global periodic tick (jiffies update)
- cpu local update_process_times
- cpu local profiling
@@ -244,6 +248,3 @@ extended to x86_64 and ARM already. Initial (work in progress) support is also
available for MIPS and PowerPC.

Thomas, Ingo
-
-
-
diff --git a/Documentation/timers/hpet.txt b/Documentation/timers/hpet.txt
index 895345ec513b..c9d05d3caaca 100644
--- a/Documentation/timers/hpet.txt
+++ b/Documentation/timers/hpet.txt
@@ -1,4 +1,6 @@
- High Precision Event Timer Driver for Linux
+===========================================
+High Precision Event Timer Driver for Linux
+===========================================

The High Precision Event Timer (HPET) hardware follows a specification
by Intel and Microsoft, revision 1.
diff --git a/Documentation/timers/hrtimers.txt b/Documentation/timers/hrtimers.txt
index 588d85724f10..c1c20a693e8f 100644
--- a/Documentation/timers/hrtimers.txt
+++ b/Documentation/timers/hrtimers.txt
@@ -1,6 +1,6 @@
-
+======================================================
hrtimers - subsystem for high-resolution kernel timers
-----------------------------------------------------
+======================================================

This patch introduces a new subsystem for high-resolution kernel timers.

@@ -146,7 +146,7 @@ the clock_getres() interface. This will return whatever real resolution
a given clock has - be it low-res, high-res, or artificially-low-res.

hrtimers - testing and verification
-----------------------------------
+-----------------------------------

We used the high-resolution clock subsystem ontop of hrtimers to verify
the hrtimer implementation details in praxis, and we also ran the posix
diff --git a/Documentation/timers/timekeeping.txt b/Documentation/timers/timekeeping.txt
index 2d1732b0a868..f83e98852e2c 100644
--- a/Documentation/timers/timekeeping.txt
+++ b/Documentation/timers/timekeeping.txt
@@ -1,5 +1,6 @@
+===========================================================
Clock sources, Clock events, sched_clock() and delay timers
------------------------------------------------------------
+===========================================================

This document tries to briefly explain some basic kernel timekeeping
abstractions. It partly pertains to the drivers usually found in
diff --git a/Documentation/timers/timers-howto.txt b/Documentation/timers/timers-howto.txt
index 038f8c77a076..7e3167bec2b1 100644
--- a/Documentation/timers/timers-howto.txt
+++ b/Documentation/timers/timers-howto.txt
@@ -1,5 +1,6 @@
+===================================================================
delays - Information on the various kernel delay / sleep mechanisms
--------------------------------------------------------------------
+===================================================================

This document seeks to answer the common question: "What is the
RightWay (TM) to insert a delay?"
@@ -17,7 +18,7 @@ code in an atomic context?" This should be followed closely by "Does
it really need to delay in atomic context?" If so...

ATOMIC CONTEXT:
- You must use the *delay family of functions. These
+ You must use the `*delay` family of functions. These
functions use the jiffie estimation of clock speed
and will busy wait for enough loop cycles to achieve
the desired delay:
@@ -35,21 +36,26 @@ ATOMIC CONTEXT:
be refactored to allow for the use of msleep.

NON-ATOMIC CONTEXT:
- You should use the *sleep[_range] family of functions.
+ You should use the `*sleep[_range]` family of functions.
There are a few more options here, while any of them may
work correctly, using the "right" sleep function will
help the scheduler, power management, and just make your
driver better :)

-- Backed by busy-wait loop:
+
udelay(unsigned long usecs)
+
-- Backed by hrtimers:
+
usleep_range(unsigned long min, unsigned long max)
+
-- Backed by jiffies / legacy_timers
+
msleep(unsigned long msecs)
msleep_interruptible(unsigned long msecs)

- Unlike the *delay family, the underlying mechanism
+ Unlike the `*delay` family, the underlying mechanism
driving each of these calls varies, thus there are
quirks you should be aware of.

@@ -70,6 +76,7 @@ NON-ATOMIC CONTEXT:
- Why not msleep for (1ms - 20ms)?
Explained originally here:
http://lkml.org/lkml/2007/8/3/250
+
msleep(1~20) may not do what the caller intends, and
will often sleep longer (~20 ms actual sleep for any
value given in the 1~20ms range). In many cases this
--
2.20.1