linux/kernel/time, branch v2.6.32.41

tick: Clear broadcast active bit when switching to oneshot

2011-05-23T18:20:19Z

commit 07f4beb0b5bbfaf36a64aa00d59e670ec578a95a upstream. The first cpu which switches from periodic to oneshot mode switches also the broadcast device into oneshot mode. The broadcast device serves as a backup for per cpu timers which stop in deeper C-states. To avoid starvation of the cpus which might be in idle and depend on broadcast mode it marks the other cpus as broadcast active and sets the brodcast expiry value of those cpus to the next tick. The oneshot mode broadcast bit for the other cpus is sticky and gets only cleared when those cpus exit idle. If a cpu was not idle while the bit got set in consequence the bit prevents that the broadcast device is armed on behalf of that cpu when it enters idle for the first time after it switched to oneshot mode. In most cases that goes unnoticed as one of the other cpus has usually a timer pending which keeps the broadcast device armed with a short timeout. Now if the only cpu which has a short timer active has the bit set then the broadcast device will not be armed on behalf of that cpu and will fire way after the expected timer expiry. In the case of Christians bug report it took ~145 seconds which is about half of the wrap around time of HPET (the limit for that device) due to the fact that all other cpus had no timers armed which expired before the 145 seconds timeframe. The solution is simply to clear the broadcast active bit unconditionally when a cpu switches to oneshot mode after the first cpu switched the broadcast device over. It's not idle at that point otherwise it would not be executing that code. [ I fundamentally hate that broadcast crap. Why the heck thought some folks that when going into deep idle it's a brilliant concept to switch off the last device which brings the cpu back from that state? ] Thanks to Christian for providing all the valuable debug information! Reported-and-tested-by: Christian Hoffmann Cc: John Stultz Link: http://lkml.kernel.org/r/%3Calpine.LFD.2.02.1105161105170.3078%40ionos%3E Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

clocksource: Install completely before selecting

2011-05-23T18:20:19Z

commit e05b2efb82596905ebfe88e8612ee81dec9b6592 upstream. Christian Hoffmann reported that the command line clocksource override with acpi_pm timer fails: Kernel command line: clocksource=acpi_pm hpet clockevent registered Switching to clocksource hpet Override clocksource acpi_pm is not HRT compatible. Cannot switch while in HRT/NOHZ mode. The watchdog code is what enables CLOCK_SOURCE_VALID_FOR_HRES, but we actually end up selecting the clocksource before we enqueue it into the watchdog list, so that's why we see the warning and fail to switch to acpi_pm timer as requested. That's particularly bad when we want to debug timekeeping related problems in early boot. Put the selection call last. Reported-by: Christian Hoffmann Signed-off-by: John Stultz Link: http://lkml.kernel.org/r/%3C1304558210.2943.24.camel%40work-vm%3E Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

Fix time() inconsistencies caused by intermediate xtime_cache values being read

2011-05-23T18:20:15Z

Currently with 2.6.32-longterm, its possible for time() to occasionally return values one second earlier then the previous time() call. This happens because update_xtime_cache() does: xtime_cache = xtime; timespec_add_ns(&xtime_cache, nsec); Its possible that xtime is 1sec,999msecs, and nsecs is 1ms, resulting in a xtime_cache that is 2sec,0ms. get_seconds() (which is used by sys_time()) does not take the xtime_lock, which is ok as the xtime.tv_sec value is a long and can be atomically read safely. The problem occurs the next call to update_xtime_cache() if xtime has not increased: /* This sets xtime_cache back to 1sec, 999msec */ xtime_cache = xtime; /* get_seconds, calls here, and sees a 1second inconsistency */ timespec_add_ns(&xtime_cache, nsec); In order to resolve this, we could add locking to get_seconds(), but it needs to be lock free, as it is called from the machine check handler, opening a possible deadlock. So instead, this patch introduces an intermediate value for the calculations, so that we only assign xtime_cache once with the correct time, using ACCESS_ONCE to make sure the compiler doesn't optimize out any intermediate values. The xtime_cache manipulations were removed with 2.6.35, so that kernel and later do not need this change. In 2.6.33 and 2.6.34 the logarithmic accumulation should make it so xtime is updated each tick, so it is unlikely that two updates to xtime_cache could occur while the difference between xtime and xtime_cache crosses the second boundary. However, the paranoid might want to pull this into 2.6.33/34-longterm just to be sure. Thanks to Stephen for helping finally narrow down the root cause and many hours of help with testing and validation. Also thanks to Max, Andi, Eric and Paul for review of earlier attempts and helping clarify what is possible with regard to out of order execution. Acked-by: Eric Dumazet Signed-off-by: John Stultz Signed-off-by: Greg Kroah-Hartman

clockevents: Prevent oneshot mode when broadcast device is periodic

2011-03-07T23:17:54Z

commit 3a142a0672b48a853f00af61f184c7341ac9c99d upstream. When the per cpu timer is marked CLOCK_EVT_FEAT_C3STOP, then we only can switch into oneshot mode, when the backup broadcast device supports oneshot mode as well. Otherwise we would try to switch the broadcast device into an unsupported mode unconditionally. This went unnoticed so far as the current available broadcast devices support oneshot mode. Seth unearthed this problem while debugging and working around an hpet related BIOS wreckage. Add the necessary check to tick_is_oneshot_available(). Reported-and-tested-by: Seth Forshee Signed-off-by: Thomas Gleixner LKML-Reference: Signed-off-by: Greg Kroah-Hartman

timekeeping: Fix clock_gettime vsyscall time warp

2010-08-13T20:20:13Z

commit 0696b711e4be45fa104c12329f617beb29c03f78 upstream. Since commit 0a544198 "timekeeping: Move NTP adjusted clock multiplier to struct timekeeper" the clock multiplier of vsyscall is updated with the unmodified clock multiplier of the clock source and not with the NTP adjusted multiplier of the timekeeper. This causes user space observerable time warps: new CLOCK-warp maximum: 120 nsecs, 00000025c337c537 -> 00000025c337c4bf Add a new argument "mult" to update_vsyscall() and hand in the timekeeping internal NTP adjusted multiplier. Signed-off-by: Lin Ming Cc: "Zhang Yanmin" Cc: Martin Schwidefsky Cc: Benjamin Herrenschmidt Cc: Tony Luck LKML-Reference: <1258436990.17765.83.camel@minggr.sh.intel.com> Signed-off-by: Thomas Gleixner Signed-off-by: Kurt Garloff Signed-off-by: Greg Kroah-Hartman

nohz: Reuse ktime in sub-functions of tick_check_idle.

2010-08-13T20:20:13Z

commit eed3b9cf3fe3fcc7a50238dfcab63a63914e8f42 upstream. On a system with NOHZ=y tick_check_idle calls tick_nohz_stop_idle and tick_nohz_update_jiffies. Given the right conditions (ts->idle_active and/or ts->tick_stopped) both function get a time stamp with ktime_get. The same time stamp can be reused if both function require one. On s390 this change has the additional benefit that gcc inlines the tick_nohz_stop_idle function into tick_check_idle. The number of instructions to execute tick_check_idle drops from 225 to 144 (without the ktime_get optimization it is 367 vs 215 instructions). before: 0) | tick_check_idle() { 0) | tick_nohz_stop_idle() { 0) | ktime_get() { 0) | read_tod_clock() { 0) 0.601 us | } 0) 1.765 us | } 0) 3.047 us | } 0) | ktime_get() { 0) | read_tod_clock() { 0) 0.570 us | } 0) 1.727 us | } 0) | tick_do_update_jiffies64() { 0) 0.609 us | } 0) 8.055 us | } after: 0) | tick_check_idle() { 0) | ktime_get() { 0) | read_tod_clock() { 0) 0.617 us | } 0) 1.773 us | } 0) | tick_do_update_jiffies64() { 0) 0.593 us | } 0) 4.477 us | } Signed-off-by: Martin Schwidefsky Cc: john stultz LKML-Reference: <20090929122533.206589318@de.ibm.com> Signed-off-by: Thomas Gleixner Acked-by: John Jolly Signed-off-by: Greg Kroah-Hartman

nohz: Introduce arch_needs_cpu

2010-08-13T20:20:13Z

commit 3c5d92a0cfb5103c0d5ab74d4ae6373d3af38148 upstream. Allow the architecture to request a normal jiffy tick when the system goes idle and tick_nohz_stop_sched_tick is called . On s390 the hook is used to prevent the system going fully idle if there has been an interrupt other than a clock comparator interrupt since the last wakeup. On s390 the HiperSockets response time for 1 connection ping-pong goes down from 42 to 34 microseconds. The CPU cost decreases by 27%. Signed-off-by: Martin Schwidefsky LKML-Reference: <20090929122533.402715150@de.ibm.com> Signed-off-by: Thomas Gleixner Acked-by: John Jolly Signed-off-by: Greg Kroah-Hartman

hrtimer: Tune hrtimer_interrupt hang logic

2010-04-01T22:58:14Z

commit 41d2e494937715d3150e5c75d01f0e75ae899337 upstream. The hrtimer_interrupt hang logic adjusts min_delta_ns based on the execution time of the hrtimer callbacks. This is error-prone for virtual machines, where a guest vcpu can be scheduled out during the execution of the callbacks (and the callbacks themselves can do operations that translate to blocking operations in the hypervisor), which in can lead to large min_delta_ns rendering the system unusable. Replace the current heuristics with something more reliable. Allow the interrupt code to try 3 times to catch up with the lost time. If that fails use the total time spent in the interrupt handler to defer the next timer interrupt so the system can catch up with other things which got delayed. Limit that deferment to 100ms. The retry events and the maximum time spent in the interrupt handler are recorded and exposed via /proc/timer_list Inspired by a patch from Marcelo. Reported-by: Michael Tokarev Signed-off-by: Thomas Gleixner Tested-by: Marcelo Tosatti Cc: kvm@vger.kernel.org Cc: Jeremy Fitzhardinge Signed-off-by: Greg Kroah-Hartman

timekeeping: Prevent oops when GENERIC_TIME=n

2010-04-01T22:58:06Z

commit ad6759fbf35d104dbf573cd6f4c6784ad6823f7e upstream. Aaro Koskinen reported an issue in kernel.org bugzilla #15366, where on non-GENERIC_TIME systems, accessing /sys/devices/system/clocksource/clocksource0/current_clocksource results in an oops. It seems the timekeeper/clocksource rework missed initializing the curr_clocksource value in the !GENERIC_TIME case. Thanks to Aaro for reporting and diagnosing the issue as well as testing the fix! Reported-by: Aaro Koskinen Signed-off-by: John Stultz Cc: Martin Schwidefsky LKML-Reference: <1267475683.4216.61.camel@localhost.localdomain> Signed-off-by: Thomas Gleixner Signed-off-by: Greg Kroah-Hartman

Export the symbol of getboottime and mmonotonic_to_bootbased

2010-02-23T15:37:52Z

commit c93d89f3dbf0202bf19c07960ca8602b48c2f9a0 upstream. Export getboottime and monotonic_to_bootbased in order to let them could be used by following patch. Signed-off-by: Jason Wang Signed-off-by: Marcelo Tosatti Signed-off-by: Greg Kroah-Hartman