docs: timers: convert docs to ReST and rename to *.rst
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. The conversion is actually: - add blank lines and identation in order to identify paragraphs; - fix tables markups; - add some lists markups; - mark literal blocks; - adjust title markups. At its new index.rst, let's add a :orphan: while this is not linked to the main index.rst file, in order to avoid build warnings. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org> Acked-by: Mark Brown <broonie@kernel.org> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
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@ -1,5 +1,6 @@
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=====================================================
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High resolution timers and dynamic ticks design notes
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-----------------------------------------------------
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=====================================================
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Further information can be found in the paper of the OLS 2006 talk "hrtimers
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and beyond". The paper is part of the OLS 2006 Proceedings Volume 1, which can
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@ -30,11 +31,12 @@ hrtimer base infrastructure
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---------------------------
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The hrtimer base infrastructure was merged into the 2.6.16 kernel. Details of
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the base implementation are covered in Documentation/timers/hrtimers.txt. See
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the base implementation are covered in Documentation/timers/hrtimers.rst. See
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also figure #2 (OLS slides p. 15)
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The main differences to the timer wheel, which holds the armed timer_list type
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timers are:
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- time ordered enqueueing into a rb-tree
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- independent of ticks (the processing is based on nanoseconds)
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@ -55,7 +57,8 @@ merged into the 2.6.18 kernel.
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Further information about the Generic Time Of Day framework is available in the
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OLS 2005 Proceedings Volume 1:
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http://www.linuxsymposium.org/2005/linuxsymposium_procv1.pdf
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http://www.linuxsymposium.org/2005/linuxsymposium_procv1.pdf
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The paper "We Are Not Getting Any Younger: A New Approach to Time and
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Timers" was written by J. Stultz, D.V. Hart, & N. Aravamudan.
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@ -100,6 +103,7 @@ accounting, profiling, and high resolution timers.
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The management layer assigns one or more of the following functions to a clock
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event device:
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- system global periodic tick (jiffies update)
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- cpu local update_process_times
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- cpu local profiling
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@ -244,6 +248,3 @@ extended to x86_64 and ARM already. Initial (work in progress) support is also
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available for MIPS and PowerPC.
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Thomas, Ingo
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@ -1,4 +1,6 @@
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High Precision Event Timer Driver for Linux
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===========================================
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High Precision Event Timer Driver for Linux
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===========================================
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The High Precision Event Timer (HPET) hardware follows a specification
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by Intel and Microsoft, revision 1.
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@ -1,6 +1,6 @@
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======================================================
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hrtimers - subsystem for high-resolution kernel timers
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----------------------------------------------------
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======================================================
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This patch introduces a new subsystem for high-resolution kernel timers.
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@ -146,7 +146,7 @@ the clock_getres() interface. This will return whatever real resolution
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a given clock has - be it low-res, high-res, or artificially-low-res.
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hrtimers - testing and verification
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----------------------------------
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-----------------------------------
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We used the high-resolution clock subsystem ontop of hrtimers to verify
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the hrtimer implementation details in praxis, and we also ran the posix
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Documentation/timers/index.rst
Normal file
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Documentation/timers/index.rst
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:orphan:
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======
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timers
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======
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.. toctree::
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:maxdepth: 1
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highres
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hpet
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hrtimers
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no_hz
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timekeeping
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timers-howto
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.. only:: subproject and html
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Indices
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=======
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* :ref:`genindex`
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@ -1,4 +1,6 @@
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NO_HZ: Reducing Scheduling-Clock Ticks
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======================================
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NO_HZ: Reducing Scheduling-Clock Ticks
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======================================
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This document describes Kconfig options and boot parameters that can
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@ -28,7 +30,8 @@ by a third section on RCU-specific considerations, a fourth section
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discussing testing, and a fifth and final section listing known issues.
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NEVER OMIT SCHEDULING-CLOCK TICKS
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Never Omit Scheduling-Clock Ticks
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=================================
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Very old versions of Linux from the 1990s and the very early 2000s
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are incapable of omitting scheduling-clock ticks. It turns out that
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@ -59,7 +62,8 @@ degrade your applications performance. If this describes your workload,
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you should read the following two sections.
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OMIT SCHEDULING-CLOCK TICKS FOR IDLE CPUs
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Omit Scheduling-Clock Ticks For Idle CPUs
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=========================================
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If a CPU is idle, there is little point in sending it a scheduling-clock
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interrupt. After all, the primary purpose of a scheduling-clock interrupt
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dyntick-idle mode.
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OMIT SCHEDULING-CLOCK TICKS FOR CPUs WITH ONLY ONE RUNNABLE TASK
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Omit Scheduling-Clock Ticks For CPUs With Only One Runnable Task
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================================================================
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If a CPU has only one runnable task, there is little point in sending it
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a scheduling-clock interrupt because there is no other task to switch to.
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(yet) be enabled by default.
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RCU IMPLICATIONS
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RCU Implications
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================
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There are situations in which idle CPUs cannot be permitted to
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enter either dyntick-idle mode or adaptive-tick mode, the most
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where you want them to run.
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TESTING
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Testing
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=======
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So you enable all the OS-jitter features described in this document,
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but do not see any change in your workload's behavior. Is this because
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systems.
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KNOWN ISSUES
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Known Issues
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============
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o Dyntick-idle slows transitions to and from idle slightly.
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* Dyntick-idle slows transitions to and from idle slightly.
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In practice, this has not been a problem except for the most
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aggressive real-time workloads, which have the option of disabling
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dyntick-idle mode, an option that most of them take. However,
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this parameter effectively disables Turbo Mode on Intel
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CPUs, which can significantly reduce maximum performance.
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o Adaptive-ticks slows user/kernel transitions slightly.
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* Adaptive-ticks slows user/kernel transitions slightly.
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This is not expected to be a problem for computationally intensive
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workloads, which have few such transitions. Careful benchmarking
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will be required to determine whether or not other workloads
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are significantly affected by this effect.
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o Adaptive-ticks does not do anything unless there is only one
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* Adaptive-ticks does not do anything unless there is only one
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runnable task for a given CPU, even though there are a number
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of other situations where the scheduling-clock tick is not
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needed. To give but one example, consider a CPU that has one
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Better handling of these sorts of situations is future work.
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o A reboot is required to reconfigure both adaptive idle and RCU
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* A reboot is required to reconfigure both adaptive idle and RCU
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callback offloading. Runtime reconfiguration could be provided
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if needed, however, due to the complexity of reconfiguring RCU at
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runtime, there would need to be an earthshakingly good reason.
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simply offloading RCU callbacks from all CPUs and pinning them
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where you want them whenever you want them pinned.
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o Additional configuration is required to deal with other sources
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* Additional configuration is required to deal with other sources
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of OS jitter, including interrupts and system-utility tasks
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and processes. This configuration normally involves binding
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interrupts and tasks to particular CPUs.
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o Some sources of OS jitter can currently be eliminated only by
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* Some sources of OS jitter can currently be eliminated only by
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constraining the workload. For example, the only way to eliminate
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OS jitter due to global TLB shootdowns is to avoid the unmapping
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operations (such as kernel module unload operations) that
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helpful, especially when combined with the mlock() and mlockall()
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system calls.
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o Unless all CPUs are idle, at least one CPU must keep the
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* Unless all CPUs are idle, at least one CPU must keep the
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scheduling-clock interrupt going in order to support accurate
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timekeeping.
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o If there might potentially be some adaptive-ticks CPUs, there
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* If there might potentially be some adaptive-ticks CPUs, there
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will be at least one CPU keeping the scheduling-clock interrupt
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going, even if all CPUs are otherwise idle.
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Better handling of this situation is ongoing work.
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o Some process-handling operations still require the occasional
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* Some process-handling operations still require the occasional
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scheduling-clock tick. These operations include calculating CPU
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load, maintaining sched average, computing CFS entity vruntime,
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computing avenrun, and carrying out load balancing. They are
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@ -1,5 +1,6 @@
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===========================================================
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Clock sources, Clock events, sched_clock() and delay timers
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-----------------------------------------------------------
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===========================================================
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This document tries to briefly explain some basic kernel timekeeping
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abstractions. It partly pertains to the drivers usually found in
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@ -1,5 +1,6 @@
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===================================================================
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delays - Information on the various kernel delay / sleep mechanisms
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-------------------------------------------------------------------
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===================================================================
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This document seeks to answer the common question: "What is the
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RightWay (TM) to insert a delay?"
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it really need to delay in atomic context?" If so...
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ATOMIC CONTEXT:
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You must use the *delay family of functions. These
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You must use the `*delay` family of functions. These
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functions use the jiffie estimation of clock speed
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and will busy wait for enough loop cycles to achieve
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the desired delay:
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be refactored to allow for the use of msleep.
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NON-ATOMIC CONTEXT:
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You should use the *sleep[_range] family of functions.
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You should use the `*sleep[_range]` family of functions.
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There are a few more options here, while any of them may
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work correctly, using the "right" sleep function will
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help the scheduler, power management, and just make your
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driver better :)
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-- Backed by busy-wait loop:
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udelay(unsigned long usecs)
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-- Backed by hrtimers:
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usleep_range(unsigned long min, unsigned long max)
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-- Backed by jiffies / legacy_timers
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msleep(unsigned long msecs)
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msleep_interruptible(unsigned long msecs)
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Unlike the *delay family, the underlying mechanism
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Unlike the `*delay` family, the underlying mechanism
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driving each of these calls varies, thus there are
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quirks you should be aware of.
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- Why not msleep for (1ms - 20ms)?
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Explained originally here:
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http://lkml.org/lkml/2007/8/3/250
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msleep(1~20) may not do what the caller intends, and
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will often sleep longer (~20 ms actual sleep for any
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value given in the 1~20ms range). In many cases this
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@ -7192,7 +7192,7 @@ F: drivers/net/ethernet/hp/hp100.*
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HPET: High Precision Event Timers driver
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M: Clemens Ladisch <clemens@ladisch.de>
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S: Maintained
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F: Documentation/timers/hpet.txt
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F: Documentation/timers/hpet.rst
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F: drivers/char/hpet.c
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F: include/linux/hpet.h
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F: include/uapi/linux/hpet.h
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/* TODO FIXME: dvb_usb_generic_rw() fails rarely with error code -32
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* (EPIPE, Broken pipe). Function supports currently msleep() as a
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* parameter but I would not like to use it, since according to
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* Documentation/timers/timers-howto.txt it should not be used such
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* Documentation/timers/timers-howto.rst it should not be used such
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* short, under < 20ms, sleeps. Repeating failed message would be
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* better choice as not to add unwanted delays...
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* Fixing that correctly is one of those or both;
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*
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* Delay for the requested amount of time as per the guidelines in:
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*
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* Documentation/timers/timers-howto.txt
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* Documentation/timers/timers-howto.rst
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*
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* The assumption here is that regulators will never be enabled in
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* atomic context and therefore sleeping functions can be used.
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* @cond: Break condition (usually involving @val)
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* @sleep_us: Maximum time to sleep between reads in us (0
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* tight-loops). Should be less than ~20ms since usleep_range
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* is used (see Documentation/timers/timers-howto.txt).
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* is used (see Documentation/timers/timers-howto.rst).
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* @timeout_us: Timeout in us, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout. In either
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* @cond: Break condition (usually involving @val)
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* @delay_us: Time to udelay between reads in us (0 tight-loops). Should
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* be less than ~10us since udelay is used (see
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* Documentation/timers/timers-howto.txt).
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* Documentation/timers/timers-howto.rst).
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* @timeout_us: Timeout in us, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout. In either
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* @cond: Break condition (usually involving @val)
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* @sleep_us: Maximum time to sleep between reads in us (0
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* tight-loops). Should be less than ~20ms since usleep_range
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* is used (see Documentation/timers/timers-howto.txt).
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* is used (see Documentation/timers/timers-howto.rst).
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* @timeout_us: Timeout in us, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout or the regmap_read
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* @cond: Break condition (usually involving @val)
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* @sleep_us: Maximum time to sleep between reads in us (0
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* tight-loops). Should be less than ~20ms since usleep_range
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* is used (see Documentation/timers/timers-howto.txt).
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* is used (see Documentation/timers/timers-howto.rst).
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* @timeout_us: Timeout in us, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout or the regmap_field_read
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@ -5712,7 +5712,7 @@ sub process {
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# ignore udelay's < 10, however
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if (! ($delay < 10) ) {
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CHK("USLEEP_RANGE",
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"usleep_range is preferred over udelay; see Documentation/timers/timers-howto.txt\n" . $herecurr);
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"usleep_range is preferred over udelay; see Documentation/timers/timers-howto.rst\n" . $herecurr);
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}
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if ($delay > 2000) {
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WARN("LONG_UDELAY",
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if ($line =~ /\bmsleep\s*\((\d+)\);/) {
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if ($1 < 20) {
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WARN("MSLEEP",
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"msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.txt\n" . $herecurr);
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"msleep < 20ms can sleep for up to 20ms; see Documentation/timers/timers-howto.rst\n" . $herecurr);
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}
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}
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my $max = $7;
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if ($min eq $max) {
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WARN("USLEEP_RANGE",
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"usleep_range should not use min == max args; see Documentation/timers/timers-howto.txt\n" . "$here\n$stat\n");
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"usleep_range should not use min == max args; see Documentation/timers/timers-howto.rst\n" . "$here\n$stat\n");
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} elsif ($min =~ /^\d+$/ && $max =~ /^\d+$/ &&
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$min > $max) {
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WARN("USLEEP_RANGE",
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"usleep_range args reversed, use min then max; see Documentation/timers/timers-howto.txt\n" . "$here\n$stat\n");
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"usleep_range args reversed, use min then max; see Documentation/timers/timers-howto.rst\n" . "$here\n$stat\n");
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}
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}
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@ -349,7 +349,7 @@ static inline const struct snd_sof_dsp_ops
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* @cond: Break condition (usually involving @val)
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* @sleep_us: Maximum time to sleep between reads in us (0
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* tight-loops). Should be less than ~20ms since usleep_range
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* is used (see Documentation/timers/timers-howto.txt).
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* is used (see Documentation/timers/timers-howto.rst).
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* @timeout_us: Timeout in us, 0 means never timeout
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*
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* Returns 0 on success and -ETIMEDOUT upon a timeout. In either
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