1. 18 Jun, 2015 12 commits
  2. 12 Jun, 2015 5 commits
    • John Stultz's avatar
      selftests: timers: Add leap-second timer edge testing to leap-a-day.c · 0c4a5fc9
      John Stultz authored
      Prarit reported an issue w/ timers around the leapsecond, where a
      timer set for Midnight UTC (00:00:00) might fire a second early right
      before the leapsecond (23:59:60 - though it appears as a repeated
      23:59:59) is applied.
      
      So I've updated the leap-a-day.c test to integrate a similar test,
      where we set a timer and check if it triggers at the right time, and
      if the ntp state transition is managed properly.
      Reported-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
      Reported-by: default avatarPrarit Bhargava <prarit@redhat.com>
      Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
      Cc: Richard Cochran <richardcochran@gmail.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Jiri Bohac <jbohac@suse.cz>
      Cc: Shuah Khan <shuahkh@osg.samsung.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Link: http://lkml.kernel.org/r/1434063297-28657-6-git-send-email-john.stultz@linaro.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      0c4a5fc9
    • John Stultz's avatar
      ntp: Do leapsecond adjustment in adjtimex read path · 96efdcf2
      John Stultz authored
      Since the leapsecond is applied at tick-time, this means there is a
      small window of time at the start of a leap-second where we cross into
      the next second before applying the leap.
      
      This patch modified adjtimex so that the leap-second is applied on the
      second edge. Providing more correct leapsecond behavior.
      
      This does make it so that adjtimex()'s returned time values can be
      inconsistent with time values read from gettimeofday() or
      clock_gettime(CLOCK_REALTIME,...)  for a brief period of one tick at
      the leapsecond.  However, those other interfaces do not provide the
      TIME_OOP time_state return that adjtimex() provides, which allows the
      leapsecond to be properly represented. They instead only see a time
      discontinuity, and cannot tell the first 23:59:59 from the repeated
      23:59:59 leap second.
      
      This seems like a reasonable tradeoff given clock_gettime() /
      gettimeofday() cannot properly represent a leapsecond, and users
      likely care more about performance, while folks who are using
      adjtimex() more likely care about leap-second correctness.
      Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
      Cc: Prarit Bhargava <prarit@redhat.com>
      Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
      Cc: Richard Cochran <richardcochran@gmail.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Jiri Bohac <jbohac@suse.cz>
      Cc: Ingo Molnar <mingo@kernel.org>
      Link: http://lkml.kernel.org/r/1434063297-28657-5-git-send-email-john.stultz@linaro.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      96efdcf2
    • John Stultz's avatar
      time: Prevent early expiry of hrtimers[CLOCK_REALTIME] at the leap second edge · 833f32d7
      John Stultz authored
      Currently, leapsecond adjustments are done at tick time. As a result,
      the leapsecond was applied at the first timer tick *after* the
      leapsecond (~1-10ms late depending on HZ), rather then exactly on the
      second edge.
      
      This was in part historical from back when we were always tick based,
      but correcting this since has been avoided since it adds extra
      conditional checks in the gettime fastpath, which has performance
      overhead.
      
      However, it was recently pointed out that ABS_TIME CLOCK_REALTIME
      timers set for right after the leapsecond could fire a second early,
      since some timers may be expired before we trigger the timekeeping
      timer, which then applies the leapsecond.
      
      This isn't quite as bad as it sounds, since behaviorally it is similar
      to what is possible w/ ntpd made leapsecond adjustments done w/o using
      the kernel discipline. Where due to latencies, timers may fire just
      prior to the settimeofday call. (Also, one should note that all
      applications using CLOCK_REALTIME timers should always be careful,
      since they are prone to quirks from settimeofday() disturbances.)
      
      However, the purpose of having the kernel do the leap adjustment is to
      avoid such latencies, so I think this is worth fixing.
      
      So in order to properly keep those timers from firing a second early,
      this patch modifies the ntp and timekeeping logic so that we keep
      enough state so that the update_base_offsets_now accessor, which
      provides the hrtimer core the current time, can check and apply the
      leapsecond adjustment on the second edge. This prevents the hrtimer
      core from expiring timers too early.
      
      This patch does not modify any other time read path, so no additional
      overhead is incurred. However, this also means that the leap-second
      continues to be applied at tick time for all other read-paths.
      
      Apologies to Richard Cochran, who pushed for similar changes years
      ago, which I resisted due to the concerns about the performance
      overhead.
      
      While I suspect this isn't extremely critical, folks who care about
      strict leap-second correctness will likely want to watch
      this. Potentially a -stable candidate eventually.
      Originally-suggested-by: default avatarRichard Cochran <richardcochran@gmail.com>
      Reported-by: default avatarDaniel Bristot de Oliveira <bristot@redhat.com>
      Reported-by: default avatarPrarit Bhargava <prarit@redhat.com>
      Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
      Cc: Richard Cochran <richardcochran@gmail.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Jiri Bohac <jbohac@suse.cz>
      Cc: Shuah Khan <shuahkh@osg.samsung.com>
      Cc: Ingo Molnar <mingo@kernel.org>
      Link: http://lkml.kernel.org/r/1434063297-28657-4-git-send-email-john.stultz@linaro.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      833f32d7
    • John Stultz's avatar
      ntp: Introduce and use SECS_PER_DAY macro instead of 86400 · 90bf361c
      John Stultz authored
      Currently the leapsecond logic uses what looks like magic values.
      
      Improve this by defining SECS_PER_DAY and using that macro
      to make the logic more clear.
      Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
      Cc: Prarit Bhargava <prarit@redhat.com>
      Cc: Daniel Bristot de Oliveira <bristot@redhat.com>
      Cc: Richard Cochran <richardcochran@gmail.com>
      Cc: Jan Kara <jack@suse.cz>
      Cc: Jiri Bohac <jbohac@suse.cz>
      Cc: Ingo Molnar <mingo@kernel.org>
      Link: http://lkml.kernel.org/r/1434063297-28657-3-git-send-email-john.stultz@linaro.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      90bf361c
    • John Stultz's avatar
      time: Move clock_was_set_seq update before updating shadow-timekeeper · d1518326
      John Stultz authored
      It was reported that 868a3e91 (hrtimer: Make offset
      update smarter) was causing timer problems after suspend/resume.
      
      The problem with that change is the modification to
      clock_was_set_seq in timekeeping_update is done prior to
      mirroring the time state to the shadow-timekeeper. Thus the
      next time we do update_wall_time() the updated sequence is
      overwritten by whats in the shadow copy.
      
      This patch moves the shadow-timekeeper mirroring to the end
      of the function, after all updates have been made, so all data
      is kept in sync.
      
      (This patch also affects the update_fast_timekeeper calls which
      were also problematically done prior to the mirroring).
      Reported-and-tested-by: default avatarJeremiah Mahler <jmmahler@gmail.com>
      Signed-off-by: default avatarJohn Stultz <john.stultz@linaro.org>
      Cc: Preeti U Murthy <preeti@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Cc: Viresh Kumar <viresh.kumar@linaro.org>
      Cc: Marcelo Tosatti <mtosatti@redhat.com>
      Cc: Frederic Weisbecker <fweisbec@gmail.com>
      Link: http://lkml.kernel.org/r/1434063297-28657-2-git-send-email-john.stultz@linaro.orgSigned-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      d1518326
  3. 10 Jun, 2015 3 commits
  4. 08 Jun, 2015 1 commit
  5. 07 Jun, 2015 6 commits
  6. 02 Jun, 2015 13 commits