linux-toradex.git/kernel/time/timer_list.c, branch v4.16-rc4

timer/debug: Change /proc/timer_list from 0444 to 0400

2017-11-13T15:04:06+00:00

While it uses %pK, there's still few reasons to read this file
as non-root.

Suggested-by: Linus Torvalds 
Acked-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar

sysrq: Reset the watchdog timers while displaying high-resolution timers

2017-03-23T19:46:53+00:00

On systems with a large number of CPUs, running sysrq- can cause
watchdog timeouts.  There are two slow sections of code in the sysrq-
path in timer_list.c.

1. print_active_timers() - This function is called by print_cpu() and
   contains a slow goto loop.  On a machine with hundreds of CPUs, this
   loop took approximately 100ms for the first CPU in a NUMA node.
   (Subsequent CPUs in the same node ran much quicker.)  The total time
   to print all of the CPUs is ultimately long enough to trigger the
   soft lockup watchdog.

2. print_tickdevice() - This function outputs a large amount of textual
   information.  This function also took approximately 100ms per CPU.

Since sysrq- is not a performance critical path, there should be no
harm in touching the nmi watchdog in both slow sections above.  Touching
it in just one location was insufficient on systems with hundreds of
CPUs as occasional timeouts were still observed during testing.

This issue was observed on an Oracle T7 machine with 128 CPUs, but I
anticipate it may affect other systems with similarly large numbers of
CPUs.

Signed-off-by: Tom Hromatka 
Reviewed-by: Rob Gardner 
Signed-off-by: John Stultz

timer_list: Remove useless cast when printing

2017-02-10T10:15:08+00:00

hrtimer_resolution is already unsigned int, not necessary to cast
it when printing.

Signed-off-by: Mars Cheng 
Cc: CC Hwang 
Cc: wsd_upstream@mediatek.com
Cc: Loda Chou 
Cc: Jades Shih 
Cc: Miles Chen 
Cc: John Stultz 
Cc: My Chuang 
Cc: Matthias Brugger 
Cc: Yingjoe Chen 
Link: http://lkml.kernel.org/r/1486626615-5879-1-git-send-email-mars.cheng@mediatek.com
Signed-off-by: Thomas Gleixner

time: Remove CONFIG_TIMER_STATS

2017-02-10T10:15:08+00:00

Currently CONFIG_TIMER_STATS exposes process information across namespaces:

kernel/time/timer_list.c print_timer():

        SEQ_printf(m, ", %s/%d", tmp, timer->start_pid);

/proc/timer_list:

 #11: <0000000000000000>, hrtimer_wakeup, S:01, do_nanosleep, cron/2570

Given that the tracer can give the same information, this patch entirely
removes CONFIG_TIMER_STATS.

Suggested-by: Thomas Gleixner 
Signed-off-by: Kees Cook 
Acked-by: John Stultz 
Cc: Nicolas Pitre 
Cc: linux-doc@vger.kernel.org
Cc: Lai Jiangshan 
Cc: Shuah Khan 
Cc: Xing Gao 
Cc: Jonathan Corbet 
Cc: Jessica Frazelle 
Cc: kernel-hardening@lists.openwall.com
Cc: Nicolas Iooss 
Cc: "Paul E. McKenney" 
Cc: Petr Mladek 
Cc: Richard Cochran 
Cc: Tejun Heo 
Cc: Michal Marek 
Cc: Josh Poimboeuf 
Cc: Dmitry Vyukov 
Cc: Oleg Nesterov 
Cc: "Eric W. Biederman" 
Cc: Olof Johansson 
Cc: Andrew Morton 
Cc: linux-api@vger.kernel.org
Cc: Arjan van de Ven 
Link: http://lkml.kernel.org/r/20170208192659.GA32582@beast
Signed-off-by: Thomas Gleixner

Replace with globally

2016-12-24T19:46:01+00:00

This was entirely automated, using the script by Al:

  PATT='^[[:blank:]]*#[[:blank:]]*include[[:blank:]]*'
  sed -i -e "s!$PATT!#include !" \
        $(git grep -l "$PATT"|grep -v ^include/linux/uaccess.h)

to do the replacement at the end of the merge window.

Requested-by: Al Viro 
Signed-off-by: Linus Torvalds

hrtimer: Handle remaining time proper for TIME_LOW_RES

2016-01-17T10:13:55+00:00

If CONFIG_TIME_LOW_RES is enabled we add a jiffie to the relative timeout to
prevent short sleeps, but we do not account for that in interfaces which
retrieve the remaining time.

Helge observed that timerfd can return a remaining time larger than the
relative timeout. That's not expected and breaks userland test programs.

Store the information that the timer was armed relative and provide functions
to adjust the remaining time. To avoid bloating the hrtimer struct make state
a u8, which as a bonus results in better code on x86 at least.

Reported-and-tested-by: Helge Deller 
Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: John Stultz 
Cc: linux-m68k@lists.linux-m68k.org
Cc: dhowells@redhat.com
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/20160114164159.273328486@linutronix.de
Signed-off-by: Thomas Gleixner

clockevents: Remove unused set_mode() callback

2015-09-14T09:00:55+00:00

All users are migrated to the per-state callbacks, get rid of the
unused interface and the core support code.

Signed-off-by: Viresh Kumar 
Signed-off-by: Thomas Gleixner 
Cc: linaro-kernel@lists.linaro.org
Cc: John Stultz 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/fd60de14cf6d125489c031207567bb255ad946f6.1441943991.git.viresh.kumar@linaro.org
Signed-off-by: Ingo Molnar

timer_list: Add the base offset so remaining nsecs are accurate for non monotonic timers

2015-08-17T18:23:31+00:00

I noticed for non-monotonic timers in timer_list, some of the
output looked a little confusing.

For example:
 #1: <0000000000000000>, posix_timer_fn, S:01, hrtimer_start_range_ns, leap-a-day/2360
 # expires at 1434412800000000000-1434412800000000000 nsecs [in 1434410725062375469 to 1434410725062375469 nsecs]

You'll note the relative time till the expiration "[in xxx to
yyy nsecs]" is incorrect. This is because its printing the delta
between CLOCK_MONOTONIC time to the CLOCK_REALTIME expiration.

This patch fixes this issue by adding the clock offset to the
"now" time which we use to calculate the delta.

Cc: Prarit Bhargava 
Cc: Daniel Bristot de Oliveira 
Cc: Richard Cochran 
Cc: Jan Kara 
Cc: Jiri Bohac 
Cc: Thomas Gleixner 
Cc: Ingo Molnar 
Cc: Shuah Khan 
Signed-off-by: John Stultz

timer: Reduce timer migration overhead if disabled

2015-06-19T13:18:28+00:00

Eric reported that the timer_migration sysctl is not really nice
performance wise as it needs to check at every timer insertion whether
the feature is enabled or not. Further the check does not live in the
timer code, so we have an extra function call which checks an extra
cache line to figure out that it is disabled.

We can do better and store that information in the per cpu (hr)timer
bases. I pondered to use a static key, but that's a nightmare to
update from the nohz code and the timer base cache line is hot anyway
when we select a timer base.

The old logic enabled the timer migration unconditionally if
CONFIG_NO_HZ was set even if nohz was disabled on the kernel command
line.

With this modification, we start off with migration disabled. The user
visible sysctl is still set to enabled. If the kernel switches to NOHZ
migration is enabled, if the user did not disable it via the sysctl
prior to the switch. If nohz=off is on the kernel command line,
migration stays disabled no matter what.

Before:
  47.76%  hog       [.] main
  14.84%  [kernel]  [k] _raw_spin_lock_irqsave
   9.55%  [kernel]  [k] _raw_spin_unlock_irqrestore
   6.71%  [kernel]  [k] mod_timer
   6.24%  [kernel]  [k] lock_timer_base.isra.38
   3.76%  [kernel]  [k] detach_if_pending
   3.71%  [kernel]  [k] del_timer
   2.50%  [kernel]  [k] internal_add_timer
   1.51%  [kernel]  [k] get_nohz_timer_target
   1.28%  [kernel]  [k] __internal_add_timer
   0.78%  [kernel]  [k] timerfn
   0.48%  [kernel]  [k] wake_up_nohz_cpu

After:
  48.10%  hog       [.] main
  15.25%  [kernel]  [k] _raw_spin_lock_irqsave
   9.76%  [kernel]  [k] _raw_spin_unlock_irqrestore
   6.50%  [kernel]  [k] mod_timer
   6.44%  [kernel]  [k] lock_timer_base.isra.38
   3.87%  [kernel]  [k] detach_if_pending
   3.80%  [kernel]  [k] del_timer
   2.67%  [kernel]  [k] internal_add_timer
   1.33%  [kernel]  [k] __internal_add_timer
   0.73%  [kernel]  [k] timerfn
   0.54%  [kernel]  [k] wake_up_nohz_cpu


Reported-by: Eric Dumazet 
Signed-off-by: Thomas Gleixner 
Cc: Peter Zijlstra 
Cc: Paul McKenney 
Cc: Frederic Weisbecker 
Cc: Viresh Kumar 
Cc: John Stultz 
Cc: Joonwoo Park 
Cc: Wenbo Wang 
Link: http://lkml.kernel.org/r/20150526224512.127050787@linutronix.de
Signed-off-by: Thomas Gleixner

clockevents: Introduce CLOCK_EVT_STATE_ONESHOT_STOPPED state

2015-05-19T14:18:02+00:00

When no timers/hrtimers are pending, the expiry time is set to a
special value: 'KTIME_MAX'. This normally happens with
NO_HZ_{IDLE|FULL} in both LOWRES/HIGHRES modes.

When 'expiry == KTIME_MAX', we either cancel the 'tick-sched' hrtimer
(NOHZ_MODE_HIGHRES) or skip reprogramming clockevent device
(NOHZ_MODE_LOWRES).  But, the clockevent device is already
reprogrammed from the tick-handler for next tick.

As the clock event device is programmed in ONESHOT mode it will at
least fire one more time (unnecessarily). Timers on few
implementations (like arm_arch_timer, etc.) only support PERIODIC mode
and their drivers emulate ONESHOT over that. Which means that on these
platforms we will get spurious interrupts periodically (at last
programmed interval rate, normally tick rate).

In order to avoid spurious interrupts, the clockevent device should be
stopped or its interrupts should be masked.

A simple (yet hacky) solution to get this fixed could be: update
hrtimer_force_reprogram() to always reprogram clockevent device and
update clockevent drivers to STOP generating events (or delay it to
max time) when 'expires' is set to KTIME_MAX. But the drawback here is
that every clockevent driver has to be hacked for this particular case
and its very easy for new ones to miss this.

However, Thomas suggested to add an optional state ONESHOT_STOPPED to
solve this problem: lkml.org/lkml/2014/5/9/508.

This patch adds support for ONESHOT_STOPPED state in clockevents
core. It will only be available to drivers that implement the
state-specific callbacks instead of the legacy ->set_mode() callback.

Signed-off-by: Viresh Kumar 
Reviewed-by: Preeti U. Murthy 
Cc: linaro-kernel@lists.linaro.org
Cc: Frederic Weisbecker 
Cc: Kevin Hilman 
Cc: Daniel Lezcano 
Cc: Peter Zijlstra 
Link: http://lkml.kernel.org/r/b8b383a03ac07b13312c16850b5106b82e4245b5.1428031396.git.viresh.kumar@linaro.org
Signed-off-by: Thomas Gleixner