• Thomas Gleixner's avatar
    [PATCH] i386 rework local apic timer calibration · d36b49b9
    Thomas Gleixner authored
    The local apic timer calibration has two problem cases:
    
    1.  The calibration is based on readout of the PIT/HPET timer to detect the
       wrap of the periodic tick.  It happens that a box gets stuck in the
       calibration loop due to a PIT with a broken readout function.
    
    2.  CoreDuo boxen show a sporadic PIT runs too slow defect, which results
       in a wrong lapic calibration.  The PIT goes back to normal operation once
       the lapic timer is switched to periodic mode.
    
    Both are existing and unfixed problems in the current upstream kernel and
    prevent certain laptops and other systems from booting Linux.
    
    Rework the code to address both problems:
    
    - Make the calibration interrupt driven.  This removes the wait_timer_tick
      magic hackery from lapic.c and time_hpet.c.  The clockevents framework
      allows easy substitution of the global tick event handler for the
      calibration.  This is more accurate than monitoring jiffies.  At this point
      of the boot process, nothing disturbes the interrupt delivery, so the
      results are very accurate.
    
    - Verify the calibration against the PM timer, when available by using the
      early access function.  When the measured calibration period is outside of
      an one percent window, then the lapic timer calibration is adjusted to the
      pm timer result.
    
    - Verify the calibration by running the lapic timer with the calibration
      handler.  Disable lapic timer in case of deviation.
    
    This also removes the "synchronization" of the local apic timer to the global
    tick.  This synchronization never worked, as there is no way to synchronize
    PIT(HPET) and local APIC timer.  The synchronization by waiting for the tick
    just alignes the local APIC timer for the first events, but later the events
    drift away due to the different clocks.  Removing the "sync" is just
    randomizing the asynchronous behaviour at setup time.
    Signed-off-by: default avatarThomas Gleixner <tglx@linutronix.de>
    Signed-off-by: default avatarIngo Molnar <mingo@elte.hu>
    Cc: Zachary Amsden <zach@vmware.com>
    Cc: "Eric W. Biederman" <ebiederm@xmission.com>
    Cc: Rohit Seth <rohitseth@google.com>
    Cc: Andi Kleen <ak@suse.de>
    Cc: john stultz <johnstul@us.ibm.com>
    Cc: Roman Zippel <zippel@linux-m68k.org>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    d36b49b9
apic.c 38.4 KB