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SubjectRe: [PATCH] ABI Documentation for /proc/timer_list, v2
Joe Korty wrote:
> Document /proc/timer_list ABI, version 2.
>
> This partially documents /timer_list, including the
> proposed 'Version 0.5' extensions that add a jiffie timer
> display.
>
> v2 exists to address some of the concerns Michael Kerrisk
> brought up. What was left out: I did not document old
> versions of /timer_list, I did not document the meaning
> of the x.y version numbering system (which only Ingo
> can answer anyway), and I did not document fields of
> secondary importance that already had adequate 'DocBook'
> documentation in the kernel sources.
>
> Signed-off-by: Joe Korty <joe.korty@ccur.com>
>
> Index: 2.6.28-rc6/Documentation/ABI/stable/procfs-timer_list
> ===================================================================
> --- /dev/null 1970-01-01 00:00:00.000000000 +0000
> +++ 2.6.28-rc6/Documentation/ABI/stable/procfs-timer_list 2008-12-01 13:07:15.000000000 -0500
> @@ -0,0 +1,129 @@
> +What: /proc/timer_list
> +Date: November 2008
> +Contact: Ingo Molnar <mingo@elte.hu>
> + Thomas Gleixner <tglx@linutronix.de>
> + Joe Korty <joe.korty@ccur.com>
> +Revision-Rate: Moderate
> +At-Revision: 0.5
> +Description:
> + /proc/timer_list displays most everything about every kind
> + of timer, and some things about time too.
> +
> + The contents of this file should be expected to change,
> + as the data displayed corresponds directly to various
> + kernel-internal data structures. For this reason, the first
> + line contains the file revision. It is the responsibility
> + of this file's maintainers to bump the revision each time a
> + kernel is released having incompatible changes in this file.
> +
> + This document covers only the version of /proc/timer_list
> + located in the kernel sources to which it is attached.
> + Documentation for previous (and later) versions of
> + /proc/timer_list is to be found (if they exist) in the
> + kernel sources of those earlier (or later) kernels.
> +
> + Section Overview
> + ----------------
> + The file contains several somewhat independent sections.
> +
> + The first section contains a few lines of global info:
> + 1 - Timer List Version: File revision.
> + 2 - HRTIMER_MAX_CLOCK_BASES: number of clock types that
> + support high resolution timers.
> + 3 - now at x nsecs: number of nsecs since boot.
> +
> + The second section is organized per-CPU. Each CPU subsection
> + in turn contains several sub-subsections which are, in order
> + of appearance:
> +
> + The contents of the data structures associated with each
> + clock on this CPU:
> + 1 - clock ID: 0 == CLOCK_REALTIME, 1 == CLOCK_MONOTONIC
> + 2 - base: kernel address of this clock's
> + hrtimer_clock_base structure.
> + 3 - resolution: resolution of this clock.
> + 4 - get_time: name of kernel function used to fetch
> + time from this clock.
> + 5 - offset: difference, in nsecs, between this clock
> + and the reference clock for this clock.
> + Under each of these clocks is, in turn, a display of all
> + the active high resolution timers queued to that clock.
> + These are the lines beginning with '#' and are described
> + in detail later in this document.

Are we supposed to be able to see lines beginning with '#' in this text file,
or only in /proc/timer_list ?

> +
> + The contents of per-CPU hrtimer data fields not
> + associated with a particular cpu clock (ie, shared by

Please use "CPU" consistenly (instead of "cpu").

> + both clocks or not associated with any clock). These
> + are: expires_next, hres_active, nr_event, nohz_mode, all
> + things idle_*, tick_stopped, last_jiffies, next_jiffies.
> + The above are field names from 'struct tick_sched' and
> + 'struct hrtimer_cpu_base', documentation for these may

'struct hrtimer_cpu_base'; documentation for these may

> + be found in the kernel DocBook.
> +
> + A display of low resolution (ie, jiffie) timer wheel
> + data. These are prefixed by the lines:
> + 1 - base: kernel virtual address of the timer wheel
> + data structure (struct tvec_base) for this cpu.
> + 2 - running timer: kernel virtual address of the
> + expired timer being processed, NULL if none.
> + 3 - timer_jiffies: what this wheel considers to
> + be the current time, will be == jiffies or
> + will lag it by a tick or two if it has not
> + caught up with the current time.
> + Also under this section is a display, one per line, of
> + each active jiffie timer queued to this CPU. These are
> + the lines under an 'active jiffie timers' section that
> + begin with a number.
> +
> + The third and final section describes each 'tick device'
> + known to the kernel. A tick device is a piece of hardware
> + capable of generating periodic and/or one-shot interrupts
> + under software control, and thus is capable of generating
> + the interrupts needed to expire the various active timers
> + at their given expiration times. Examples of tick devices:
> + hpet, pit, lapic. All but the first two lines display
> + fields corresponding to structure elements from 'struct
> + clock_event_device', documentation for which can be found
> + in the kernel Docbook. The first two lines are:
> + 1 - mode: 0 == periodic timer, 1 == one-shot timer
> + 2 - is 'Per CPU device' or is 'Broadcast device'
> +
> + Hires Timer Layout
> + ------------------
> + High-resolution timers are displayed on lines that begin
> + with a '#' and always appear under one of the many sections
> + labeled 'active timers'. There is an 'active timers'
> + section for every CPU and every clock.
> +
> + The fields of a hrtimer, spread out over two lines, are:

an hrtimer,
> +
> + line 1 fields:
> + 1 - unique hrtimer index (#0, #1, #2, etc)
> + 2 - kernel address of the hrtimer data structure
> + in question
> + 3 - function to be called when timer expires
> + 4 - timer state (eg, S:01), avail states, OR-able:
> + 0 - inactive
> + 1 - enqueued
> + 2 - callback
> + 4 - pending
> + 8 - migrate
> + 5 - function which created the timer
> + 6 - process name & pid which created the timer
> +
> + line 2 fields:
> + 1 - absolute expiration time, range format (start - end)
> + 2 - relative expiration time, range format (start - end)
> +
> + Lowres Timer Layout
> + -------------------
> + Low-resolution timers are displayed one-per-line under
> + sections labeled 'active jiffie timers'. There is one such
> + section per CPU. A lowres timer has the following fields:
> +
> + 1 - number of jiffies remaining until timer expires
> + 2 - function to be called on expiration
> + 3 - data value to be given to the above function on
> + expiration
> + 4 - function which created this timer
> + 5 - name & pid of the process that created this timer


Thanks,
~Randy


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