linux/kernel/time
John Stultz da8b44d5a9 timer: convert timer_slack_ns from unsigned long to u64
This patchset introduces a /proc/<pid>/timerslack_ns interface which
would allow controlling processes to be able to set the timerslack value
on other processes in order to save power by avoiding wakeups (Something
Android currently does via out-of-tree patches).

The first patch tries to fix the internal timer_slack_ns usage which was
defined as a long, which limits the slack range to ~4 seconds on 32bit
systems.  It converts it to a u64, which provides the same basically
unlimited slack (500 years) on both 32bit and 64bit machines.

The second patch introduces the /proc/<pid>/timerslack_ns interface
which allows the full 64bit slack range for a task to be read or set on
both 32bit and 64bit machines.

With these two patches, on a 32bit machine, after setting the slack on
bash to 10 seconds:

$ time sleep 1

real    0m10.747s
user    0m0.001s
sys     0m0.005s

The first patch is a little ugly, since I had to chase the slack delta
arguments through a number of functions converting them to u64s.  Let me
know if it makes sense to break that up more or not.

Other than that things are fairly straightforward.

This patch (of 2):

The timer_slack_ns value in the task struct is currently a unsigned
long.  This means that on 32bit applications, the maximum slack is just
over 4 seconds.  However, on 64bit machines, its much much larger (~500
years).

This disparity could make application development a little (as well as
the default_slack) to a u64.  This means both 32bit and 64bit systems
have the same effective internal slack range.

Now the existing ABI via PR_GET_TIMERSLACK and PR_SET_TIMERSLACK specify
the interface as a unsigned long, so we preserve that limitation on
32bit systems, where SET_TIMERSLACK can only set the slack to a unsigned
long value, and GET_TIMERSLACK will return ULONG_MAX if the slack is
actually larger then what can be stored by an unsigned long.

This patch also modifies hrtimer functions which specified the slack
delta as a unsigned long.

Signed-off-by: John Stultz <john.stultz@linaro.org>
Cc: Arjan van de Ven <arjan@linux.intel.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Oren Laadan <orenl@cellrox.com>
Cc: Ruchi Kandoi <kandoiruchi@google.com>
Cc: Rom Lemarchand <romlem@android.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Android Kernel Team <kernel-team@android.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2016-03-17 15:09:34 -07:00
..
alarmtimer.c alarmtimer: Avoid unexpected rtc interrupt when system resume from S3 2015-12-03 22:31:42 -08:00
clockevents.c clockevents: Remove unused set_mode() callback 2015-09-14 11:00:55 +02:00
clocksource.c clocksource: Allow unregistering the watchdog 2016-01-27 12:38:05 +01:00
hrtimer.c timer: convert timer_slack_ns from unsigned long to u64 2016-03-17 15:09:34 -07:00
itimer.c itimers: Handle relative timers with CONFIG_TIME_LOW_RES proper 2016-01-17 11:13:55 +01:00
jiffies.c jiffies: Use CLOCKSOURCE_MASK instead of constant 2016-02-27 08:55:31 +01:00
Kconfig rcu: Drop RCU_USER_QS in favor of NO_HZ_FULL 2015-07-06 13:52:18 -07:00
Makefile time: Remove development rules from Kbuild/Makefile 2015-07-01 09:57:35 +02:00
ntp_internal.h ntp: Fix second_overflow's input parameter type to be 64bits 2015-12-16 16:50:56 -08:00
ntp.c ntp: Fix ADJ_SETOFFSET being used w/ ADJ_NANO 2016-01-22 12:01:42 +01:00
posix-clock.c posix-clock: Fix return code on the poll method's error path 2015-12-29 11:33:06 +01:00
posix-cpu-timers.c posix-cpu-timers: Migrate to use new tick dependency mask model 2016-03-02 16:44:27 +01:00
posix-timers.c posix-timers: Handle relative timers with CONFIG_TIME_LOW_RES proper 2016-01-17 11:13:55 +01:00
sched_clock.c timers, sched/clock: Clean up the code a bit 2015-03-27 08:34:01 +01:00
test_udelay.c time: Rename udelay_test.c to test_udelay.c 2014-11-21 11:59:55 -08:00
tick-broadcast-hrtimer.c kernel: broadcast-hrtimer: Migrate to new 'set-state' interface 2015-08-10 11:41:08 +02:00
tick-broadcast.c tick: Move the export of tick_broadcast_oneshot_control to the proper place 2015-07-14 12:01:04 +02:00
tick-common.c clockevents: Remove unused set_mode() callback 2015-09-14 11:00:55 +02:00
tick-internal.h timer: Minimize nohz off overhead 2015-06-19 15:18:28 +02:00
tick-oneshot.c clockevents: Provide functions to set and get the state 2015-06-02 14:40:47 +02:00
tick-sched.c sched-clock: Migrate to use new tick dependency mask model 2016-03-02 16:44:57 +01:00
tick-sched.h nohz: New tick dependency mask 2016-03-02 16:41:39 +01:00
time.c Merge branch 'timers-core-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip 2015-09-01 14:04:50 -07:00
timeconst.bc timeconst: Update path in comment 2015-10-26 10:06:06 +09:00
timeconv.c time: add function to convert between calendar time and broken-down time for universal use 2009-09-24 07:20:56 -07:00
timecounter.c timecounter: keep track of accumulated fractional nanoseconds 2014-12-30 18:29:27 -05:00
timekeeping_debug.c timekeeping: Convert timekeeping core to use timespec64s 2014-07-23 10:17:54 -07:00
timekeeping_internal.h clocksource: Make clocksource validation work for all clocksources 2015-12-19 15:59:57 +01:00
timekeeping.c time/timekeeping: Work around false positive GCC warning 2016-03-08 11:09:53 +01:00
timekeeping.h hrtimer: Make offset update smarter 2015-04-22 17:06:49 +02:00
timer_list.c hrtimer: Handle remaining time proper for TIME_LOW_RES 2016-01-17 11:13:55 +01:00
timer_stats.c timer: Stats: Simplify the flags handling 2015-06-19 15:18:27 +02:00
timer.c timer: convert timer_slack_ns from unsigned long to u64 2016-03-17 15:09:34 -07:00