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  1. 16 Oct, 2007 1 commit
    • Ingo Molnar's avatar
      time: introduce xtime_seconds · f20bf612
      Ingo Molnar authored
      improve performance of sys_time(). sys_time() returns time in seconds,
      but it does so by calling do_gettimeofday() and then returning the
      tv_sec portion of the GTOD time. But the data structure "xtime", which
      is updated by every timer/scheduler tick, already offers HZ granularity
      time.
      
      the patch improves the sysbench oltp macrobenchmark by 4-5% on an AMD
      dual-core system:
      
      v2.6.23:
      
      #threads
      
         1:     transactions:                        4073   (407.23 per sec.)
         2:     transactions:                        8530   (852.81 per sec.)
         3:     transactions:                        8321   (831.88 per sec.)
         4:     transactions:                        8407   (840.58 per sec.)
         5:     transactions:                        8070   (806.74 per sec.)
      
      v2.6.23 + sys_time-speedup.patch:
      
         1:     transactions:                        4281   (428.09 per sec.)
         2:     transactions:                        8910   (890.85 per sec.)
         3:     transactions:                        8659   (865.79 per sec.)
         4:     transactions:                        8676   (867.34 per sec.)
         5:     transactions:                        8532   (852.91 per sec.)
      
      and by 4-5% on an Intel dual-core system too:
      
      2.6.23:
      
        1:     transactions:                        4560   (455.94 per sec.)
        2:     transactions:                        10094  (1009.30 per sec.)
        3:     transactions:                        9755   (975.36 per sec.)
        4:     transactions:                        9859   (985.78 per sec.)
        5:     transactions:                        9701   (969.72 per sec.)
      
      2.6.23 + sys_time-speedup.patch:
      
        1:     transactions:                        4779   (477.84 per sec.)
        2:     transactions:                        10103  (1010.14 per sec.)
        3:     transactions:                        10141  (1013.93 per sec.)
        4:     transactions:                        10371  (1036.89 per sec.)
        5:     transactions:                        10178  (1017.50 per sec.)
      
      (the more CPUs the system has, the more speedup this patch gives for
      this particular workload.)
      Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      f20bf612
  2. 16 Sep, 2007 2 commits
    • Thomas Gleixner's avatar
      timekeeping: Prevent time going backwards on resume · 6a669ee8
      Thomas Gleixner authored
      Timekeeping resume adjusts xtime by adding the slept time in seconds and
      resets the reference value of the clock source (clock->cycle_last).
      clock->cycle last is used to calculate the delta between the last xtime
      update and the readout of the clock source in __get_nsec_offset(). xtime
      plus the offset is the current time. The resume code ignores the delta
      which had already elapsed between the last xtime update and the actual
      time of suspend. If the suspend time is short, then we can see time
      going backwards on resume.
      
      Suspend:
      offs_s = clock->read() - clock->cycle_last;
      now = xtime + offs_s;
      timekeeping_suspend_time = read_rtc();
      
      Resume:
      sleep_time = read_rtc() - timekeeping_suspend_time;
      xtime.tv_sec += sleep_time;
      clock->cycle_last = clock->read();
      offs_r = clock->read() - clock->cycle_last;
      now = xtime + offs_r;
      
      if sleep_time_seconds == 0 and offs_r < offs_s, then time goes
      backwards.
      
      Fix this by storing the offset from the last xtime update and add it to
      xtime during resume, when we reset clock->cycle_last:
      
      sleep_time = read_rtc() - timekeeping_suspend_time;
      xtime.tv_sec += sleep_time;
      xtime += offs_s;	/* Fixup xtime offset at suspend time */
      clock->cycle_last = clock->read();
      offs_r = clock->read() - clock->cycle_last;
      now = xtime + offs_r;
      
      Thanks to Marcelo for tracking this down on the OLPC and providing the
      necessary details to analyze the root cause.
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: John Stultz <johnstul@us.ibm.com>
      Cc: Tosatti <marcelo@kvack.org>
      6a669ee8
    • Thomas Gleixner's avatar
      timekeeping: access rtc outside of xtime lock · 3be90950
      Thomas Gleixner authored
      Lockdep complains about the access of rtc in timekeeping_suspend
      inside the interrupt disabled region of the write locked xtime lock.
      Move the access outside.
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      Cc: John Stultz <johnstul@us.ibm.com>
      3be90950
  3. 25 Jul, 2007 2 commits
    • john stultz's avatar
      Cache xtime every call to update_wall_time · 17c38b74
      john stultz authored
      This avoids xtime lag seen with dynticks, because while 'xtime' itself
      is still not updated often, we keep a 'xtime_cache' variable around that
      contains the approximate real-time that _is_ updated each time we do a
      'update_wall_time()', and is thus never off by more than one tick.
      
      IOW, this restores the original semantics for 'xtime' users, as long as
      you use the proper abstraction functions (ie 'current_kernel_time()' or
      'get_seconds()' depending on whether you want a timespec or just the
      seconds field).
      
      [ Updated Patch.  As penance for my sins I've also yanked another #ifdef
        that was added to avoid the xtime lag w/ hrtimers.  ]
      Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      17c38b74
    • john stultz's avatar
      Cleanup non-arch xtime uses, use get_seconds() or current_kernel_time(). · 2c6b47de
      john stultz authored
      This avoids use of the kernel-internal "xtime" variable directly outside
      of the actual time-related functions.  Instead, use the helper functions
      that we already have available to us.
      
      This doesn't actually change any behaviour, but this will allow us to
      fix the fact that "xtime" isn't updated very often with CONFIG_NO_HZ
      (because much of the realtime information is maintained as separate
      offsets to 'xtime'), which has caused interfaces that use xtime directly
      to get a time that is out of sync with the real-time clock by up to a
      third of a second or so.
      Signed-off-by: default avatarJohn Stultz <johnstul@us.ibm.com>
      Cc: Ingo Molnar <mingo@elte.hu>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      2c6b47de
  4. 20 Jul, 2007 1 commit
  5. 19 Jul, 2007 1 commit
  6. 16 Jul, 2007 1 commit
    • Tomas Janousek's avatar
      Introduce boot based time · 7c3f1a57
      Tomas Janousek authored
      The commits
      
        411187fb (GTOD: persistent clock support)
        c1d370e1 (i386: use GTOD persistent clock
          support)
      
      changed the monotonic time so that it no longer jumps after resume, but it's
      not possible to use it for boot time and process start time calculations then.
       Also, the uptime no longer increases during suspend.
      
      I add a variable to track the wall_to_monotonic changes, a function to get the
      real boot time and a function to get the boot based time from the monotonic
      one.
      
      [akpm@linux-foundation.org: remove exports, add comment]
      Signed-off-by: default avatarTomas Janousek <tjanouse@redhat.com>
      Cc: Tomas Smetana <tsmetana@redhat.com>
      Cc: John Stultz <johnstul@us.ibm.com>
      Cc: Thomas Gleixner <tglx@linutronix.de>
      Cc: Ingo Molnar <mingo@elte.hu>
      Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
      Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
      7c3f1a57
  7. 14 May, 2007 1 commit
  8. 08 May, 2007 1 commit