linux/kernel/time/timekeeping.c, branch v2.6.31-rc3

Merge branch 'master' of git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6

2009-06-11T06:01:14Z

sched, timers: move calc_load() to scheduler

2009-05-15T13:32:45Z

Dimitri Sivanich noticed that xtime_lock is held write locked across calc_load() which iterates over all online CPUs. That can cause long latencies for xtime_lock readers on large SMP systems. The load average calculation is an rough estimate anyway so there is no real need to protect the readers vs. the update. It's not a problem when the avenrun array is updated while a reader copies the values. Instead of iterating over all online CPUs let the scheduler_tick code update the number of active tasks shortly before the avenrun update happens. The avenrun update itself is handled by the CPU which calls do_timer(). [ Impact: reduce xtime_lock write locked section ] Signed-off-by: Thomas Gleixner Acked-by: Peter Zijlstra

timekeeping: create arch_gettimeoffset infrastructure

2009-05-02T09:45:15Z

Some arches don't supply their own clocksource. This is mainly the case in architectures that get their inter-tick times by reading the counter on their interval timer. Since these timers wrap every tick, they're not really useful as clocksources. Wrapping them to act like one is possible but not very efficient. So we provide a callout these arches can implement for use with the jiffies clocksource to provide finer then tick granular time. [ Impact: ease the migration to generic time keeping ] Signed-off-by: John Stultz Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner

clocksource: add enable() and disable() callbacks

2009-04-21T20:41:47Z

Add enable() and disable() callbacks for clocksources. This allows us to put unused clocksources in power save mode. The functions clocksource_enable() and clocksource_disable() wrap the callbacks and are inserted in the timekeeping code to enable before use and disable after switching to a new clocksource. Signed-off-by: Magnus Damm Acked-by: John Stultz Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds

sched_clock: prevent scd->clock from moving backwards, take #2

2008-12-31T08:53:21Z

Redo: 5b7dba4: sched_clock: prevent scd->clock from moving backwards which had to be reverted due to s2ram hangs: ca7e716: Revert "sched_clock: prevent scd->clock from moving backwards" ... this time with resume restoring GTOD later in the sequence taken into account as well. The "timekeeping_suspended" flag is not very nice but we cannot call into GTOD before it has been properly resumed and the scheduler will run very early in the resume sequence. Cc: Signed-off-by: Ingo Molnar

time: catch xtime_nsec underflows and fix them

2008-12-04T07:43:02Z

Impact: fix time warp bug Alex Shi, along with Yanmin Zhang have been noticing occasional time inconsistencies recently. Through their great diagnosis, they found that the xtime_nsec value used in update_wall_time was occasionally going negative. After looking through the code for awhile, I realized we have the possibility for an underflow when three conditions are met in update_wall_time(): 1) We have accumulated a second's worth of nanoseconds, so we incremented xtime.tv_sec and appropriately decrement xtime_nsec. (This doesn't cause xtime_nsec to go negative, but it can cause it to be small). 2) The remaining offset value is large, but just slightly less then cycle_interval. 3) clocksource_adjust() is speeding up the clock, causing a corrective amount (compensating for the increase in the multiplier being multiplied against the unaccumulated offset value) to be subtracted from xtime_nsec. This can cause xtime_nsec to underflow. Unfortunately, since we notify the NTP subsystem via second_overflow() whenever we accumulate a full second, and this effects the error accumulation that has already occured, we cannot simply revert the accumulated second from xtime nor move the second accumulation to after the clocksource_adjust call without a change in behavior. This leaves us with (at least) two options: 1) Simply return from clocksource_adjust() without making a change if we notice the adjustment would cause xtime_nsec to go negative. This would work, but I'm concerned that if a large adjustment was needed (due to the error being large), it may be possible to get stuck with an ever increasing error that becomes too large to correct (since it may always force xtime_nsec negative). This may just be paranoia on my part. 2) Catch xtime_nsec if it is negative, then add back the amount its negative to both xtime_nsec and the error. This second method is consistent with how we've handled earlier rounding issues, and also has the benefit that the error being added is always in the oposite direction also always equal or smaller then the correction being applied. So the risk of a corner case where things get out of control is lessened. This patch fixes bug 11970, as tested by Yanmin Zhang http://bugzilla.kernel.org/show_bug.cgi?id=11970 Reported-by: alex.shi@intel.com Signed-off-by: John Stultz Acked-by: "Zhang, Yanmin" Tested-by: "Zhang, Yanmin" Signed-off-by: Ingo Molnar

Merge branches 'timers/clocksource', 'timers/hrtimers', 'timers/nohz', 'timers/ntp', 'timers/posixtimers' and 'timers/debug' into v28-timers-for-linus

2008-10-20T11:14:06Z

timekeeping: fix rounding problem during clock update

2008-09-24T15:33:13Z

Due to a rounding problem during a clock update it's possible for readers to observe the clock jumping back by 1nsec. The following simplified example demonstrates the problem: cycle xtime 0 0 1000 999999.6 2000 1999999.2 3000 2999998.8 ... 1500 = 1499999.4 = 0.0 + 1499999.4 = 999999.6 + 499999.8 When reading the clock only the full nanosecond part is used, while timekeeping internally keeps nanosecond fractions. If the clock is now updated at cycle 1500 here, a nanosecond is missing due to the truncation. The simple fix is to round up the xtime value during the update, this also changes the distance to the reference time, but the adjustment will automatically take care that it stays under control. Signed-off-by: Roman Zippel Signed-off-by: John Stultz Signed-off-by: Andrew Morton Signed-off-by: Thomas Gleixner

clocksource: introduce CLOCK_MONOTONIC_RAW

2008-08-21T07:50:24Z

In talking with Josip Loncaric, and his work on clock synchronization (see btime.sf.net), he mentioned that for really close synchronization, it is useful to have access to "hardware time", that is a notion of time that is not in any way adjusted by the clock slewing done to keep close time sync. Part of the issue is if we are using the kernel's ntp adjusted representation of time in order to measure how we should correct time, we can run into what Paul McKenney aptly described as "Painting a road using the lines we're painting as the guide". I had been thinking of a similar problem, and was trying to come up with a way to give users access to a purely hardware based time representation that avoided users having to know the underlying frequency and mask values needed to deal with the wide variety of possible underlying hardware counters. My solution is to introduce CLOCK_MONOTONIC_RAW. This exposes a nanosecond based time value, that increments starting at bootup and has no frequency adjustments made to it what so ever. The time is accessed from userspace via the posix_clock_gettime() syscall, passing CLOCK_MONOTONIC_RAW as the clock_id. Signed-off-by: John Stultz Signed-off-by: Roman Zippel Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar

clocksource: introduce clocksource_forward_now()

2008-08-21T07:50:24Z

To keep the raw monotonic patch simple first introduce clocksource_forward_now(), which takes care of the offset since the last update_wall_time() call and adds it to the clock, so there is no need anymore to deal with it explicitly at various places, which need to make significant changes to the clock. This is also gets rid of the timekeeping_suspend_nsecs, instead of waiting until resume, the value is accumulated during suspend. In the end there is only a single user of __get_nsec_offset() left, so I integrated it back to getnstimeofday(). Signed-off-by: Roman Zippel Signed-off-by: Andrew Morton Signed-off-by: Ingo Molnar