Commit Graph

18 Commits

Author SHA1 Message Date
Paul E. McKenney ce5f4fc861 nohz_full: Document additional restrictions
This commit calls out the potential for slowing the tick even when there
are multiple runnable processes per CPU,  It also points out that current
mainlined version keeps the tick going on at least one CPU even when all
CPUs are otherwise idle.  Finally, it notes the need for a 1-HZ tick in
order to calculate CPU load, maintain sched average, compute CFS entity
vruntime, compute avenrun, and carry out load balancing.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10 13:42:38 -07:00
Paul E. McKenney 295fde89be nohz_full: Update based on Sedat Dilek review
Make it more clear that there are three options, and give hints as
to which of the three is most likely to be useful in different
situations.

Reported-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Reviewed-by: Josh Triplett <josh@joshtriplett.org>
2013-06-10 13:42:37 -07:00
Paul E. McKenney 0c87f9b5ca nohz_full: Add documentation.
Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Kevin Hilman <khilman@linaro.org>
Cc: Christoph Lameter <cl@linux.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Olivier Baetz <olivier.baetz@novasparks.com>
Reviewed-by: Randy Dunlap <rdunlap@infradead.org>
Reviewed-by: Borislav Petkov <bp@suse.de>
Reviewed-by: Kevin Hilman <khilman@linaro.org>
2013-04-27 16:41:43 -07:00
Paul Bolle 395cf9691d doc: fix broken references
There are numerous broken references to Documentation files (in other
Documentation files, in comments, etc.). These broken references are
caused by typo's in the references, and by renames or removals of the
Documentation files. Some broken references are simply odd.

Fix these broken references, sometimes by dropping the irrelevant text
they were part of.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-09-27 18:08:04 +02:00
Jonathan Neuschäfer 049262940e doc: timers-howto: fix a typo ("unsgined")
Signed-off-by: Jonathan Neuschäfer <j.neuschaefer@gmx.net>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2011-05-17 10:52:02 +02:00
Uwe Kleine-König b595076a18 tree-wide: fix comment/printk typos
"gadget", "through", "command", "maintain", "maintain", "controller", "address",
"between", "initiali[zs]e", "instead", "function", "select", "already",
"equal", "access", "management", "hierarchy", "registration", "interest",
"relative", "memory", "offset", "already",

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2010-11-01 15:38:34 -04:00
Jaswinder Singh Rajput aaaddfe0b3 Documentation/timers/hpet_example.c: add supporting info for hpet_example
$./hpet_example info /dev/hpet
-hpet: executing info
hpet_info: hi_irqfreq 0x0 hi_flags 0x0 hi_hpet 0 hi_timer 2

Signed-off-by: Jaswinder Singh Rajput <jaswinderrajput@gmail.com>
Cc: Clemens Ladisch <clemens@ladisch.de>
Cc: "Venkatesh Pallipadi (Venki)" <venki@google.com>
Cc: john stultz <johnstul@us.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-10-26 16:52:11 -07:00
Patrick Pannuto 0fcb80818b Documentation: Add timers/timers-howto.txt
This file seeks to explain the nuances in various delays;
many driver writers are not necessarily familiar with the
various kernel timers, their shortfalls, and quirks. When
faced with

ndelay, udelay, mdelay, usleep_range, msleep, and msleep_interrubtible

the question "How do I just wait 1 ms for my hardware to
latch?" has the non-intuitive "best" answer:
	usleep_range(1000,1500)

This patch is followed by a series of checkpatch additions
that seek to help kernel hackers pick the best delay.

Signed-off-by: Patrick Pannuto <ppannuto@codeaurora.org>
Cc: apw@canonical.com
Cc: corbet@lwn.net
Cc: arjan@linux.intel.com
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Andrew Morton <akpm@linux-foundation.org>
LKML-Reference: <1280786467-26999-3-git-send-email-ppannuto@codeaurora.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2010-08-04 11:00:45 +02:00
Randy Dunlap 0a6531ebea Documentation/timers/hpet_example.c: only build on X86
We should only build hpet_example on x86[-64], where it is implemented.
It can cause build errors on other architectures.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Reported-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Heiko Carstens <heiko.carstens@de.ibm.com>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-06-01 10:05:19 -07:00
Andrea Gelmini 4164fcc2f9 Documentation/timers/hpet_example: drop duplicate header files
Documentation/timers/hpet_example.c: fcntl.h is included more than once.
Documentation/timers/hpet_example.c: signal.h is included more than once.

Signed-off-by: Andrea Gelmini <andrea.gelmini@gelma.net>
Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-05-24 07:30:56 -07:00
Randy Dunlap e61863099f Documentation/timers/: split txt and source files
Documentation/timers/hpet.txt:
Expose example and tool source files in the Documentation/timers/ directory in
their own files instead of being buried (almost hidden) in readme/txt files.
This should help to prevent bitrot.

This will make them more visible/usable to users who may need
to use them, to developers who may need to test with them, and
to anyone who would fix/update them if they were more visible.

Also, if any of these possibly should not be in the kernel tree at
all, it will be clearer that they are here and we can discuss if
they should be removed.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2010-03-12 15:52:35 -08:00
Amerigo Wang 1039c6ba67 fix URL in hpet.txt
That URL is out of date. Update it.

Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Randy Dunlap <rdunlap@xenotime.net>
Cc: Matt LaPlante <kernel1@cyberdogtech.com>
Cc: Jiri Kosina <jkosina@suse.cz>
Signed-off-by: WANG Cong <amwang@redhat.com>
Acked-by: Matt LaPlante <kernel@cyberdogtech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2009-11-09 09:40:54 +01:00
Matt LaPlante 19f5946001 trivial: Miscellaneous documentation typo fixes
Fix various typos in documentation txts.

Signed-off-by: Matt LaPlante <kernel1@cyberdogtech.com>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>
2009-06-12 18:01:47 +02:00
David Brownell 64a76f667d hpet: /dev/hpet - fixes and cleanup
Minor /dev/hpet updates and bugfixes:

  * Remove dead code, mostly remnants of an incomplete/unusable
    kernel interface ... noted when addressing "sparse" warnings:
      + hpet_unregister() and a routine it calls
      + hpet_task and all references, including hpet_task_lock
      + hpet_data.hd_flags (and HPET_DATA_PLATFORM)

  * Correct and improve boot message:
      + displays *counter* (shared between comparators) bit width,
        not *timer* bit widths (which are often mixed)
      + relabel "timers" as "comparators"; this is less confusing,
        they are not independent like normal timers are (sigh)
      + display MHz not Hz; it's never less than 10 MHz.

  * Tighten and correct the userspace interface code
      + don't accidentally program comparators in 64-bit mode using
        32-bit values ... always force comparators into 32-bit mode
      + provide the correct bit definition flagging comparators with
        periodic capability ... the ABI is unchanged

  * Update Documentation/hpet.txt
      + be more correct and current
      + expand description a bit
      + don't mention that now-gone kernel interface

Plus, add a FIXME comment for something that could cause big trouble
on systems with more capable HPETs than at least Intel seems to ship.

It seems that few folk use this userspace interface; it's not very
usable given the general lack of HPET IRQ routing.  I'm told that
the only real point of it any more is to mmap for fast timestamps;
IMO that's handled better through the gettimeofday() vsyscall.

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Acked-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
2008-07-31 18:45:41 +02:00
Ingo Molnar 85e9ca333d Merge branch 'linus' into timers/hpet 2008-07-31 18:43:41 +02:00
Matt LaPlante d91958815d Documentation cleanup: trivial misspelling, punctuation, and grammar corrections.
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2008-07-26 12:00:06 -07:00
Randy Dunlap a300bec952 documentation: move hpet.txt to timers/ subdirectory
Move hpet.txt to Documentation/timers/ subdirectory.
Add 00-INDEX to Documentation/timers/ subdirectory.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: tglx <tglx@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-07-24 01:32:41 +02:00
Thomas Gleixner 3833eecc18 Documentation: move timer related documentation to a single place
We have two directories with timer related information in
Documentation/: hrtimers/ and hrtimer/. timer_stats are not restricted
to hrtimers. Move all those files into Documentation/timers where we
can pile up other timer related docs as well.

Pointed-out-by: Randy Dunlap <randy@oracle.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
2008-04-17 12:22:31 +02:00