1. 29 Apr, 2011 1 commit
    • Thomas Gleixner's avatar
      hrtimer: Initialize CLOCK_ID to HRTIMER_BASE table statically · ce31332d
      Thomas Gleixner authored
      Sedat and Bruno reported RCU stalls which turned out to be caused by
      the following;
      
      sched_init() calls init_rt_bandwidth() which calls hrtimer_init()
      _BEFORE_ hrtimers_init() is called. While not entirely correct this
      worked because hrtimer_init() only accessed statically initialized
      data (hrtimer_bases.clock_base[CLOCK_MONOTONIC])
      
      Commit e06383db (hrtimers: extend hrtimer base code to handle more
      then 2 clockids) added an indirection to the hrtimer_bases.clock_base
      lookup to avoid gap handling in the hot path. The table which is used
      for the translataion from CLOCK_ID to HRTIMER_BASE index is
      initialized at runtime in hrtimers_init(). So the early call of the
      scheduler code translates CLOCK_MONOTONIC to HRTIMER_BASE_REALTIME.
      
      Thus the rt_bandwith timer ends up on CLOCK_REALTIME. If the timer is
      armed and the wall clock time is set (e.g. ntpdate in the early boot
      process - which also gives the problem deterministic behaviour
      i.e. magic recovery after N hours), then the timer ends up with an
      expiry time far into the future. That breaks the RT throttler
      mechanism as rt runtime is accumulated and never cleared, so the rt
      throttler detects a false cpu hog condition and blocks all RT tasks
      until the timer finally expires. That in turn stalls the RCU thread of
      TINYRCU which leads to an huge amount of RCU callbacks piling up.
      
      Make the translation table statically initialized, so we are back to
      the status of <= 2.6.39.
      Reported-and-tested-by: default avatarSedat Dilek <sedat.dilek@gmail.com>
      Reported-by: default avatarBruno Prémont <bonbons@linux-vserver.org>
      Cc: John stultz <johnstul@us.ibm.com>
      Cc: Mike Galbraith <efault@gmx.de>
      Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
      Cc: Peter Zijlstra <peterz@infradead.org>
      Link: http://lkml.kernel.org/r/%3Calpine.LFD.2.02.1104282353140.3005%40ionos%3EReviewed-by: default avatarIngo Molnar <mingo@elte.hu>
      Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
      ce31332d
  2. 28 Apr, 2011 1 commit
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  4. 26 Apr, 2011 17 commits
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  6. 24 Apr, 2011 1 commit