lkml.org 
[lkml]   [2006]   [Nov]   [9]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    Patch in this message
    /
    Date
    From
    Subject[patch 13/19] GTOD: Mark TSC unusable for highres timers
    From: Thomas Gleixner <tglx@linutronix.de>

    The TSC is too unstable and unreliable to be used with high resolution timers.
    The automatic detection of TSC unstability fails once we switched to high
    resolution mode, because the tick emulation would use the TSC as reference.
    This results in a circular dependency. Mark it unusable for high res upfront.

    [akpm@osdl.org: updated for i386-time-avoid-pit-smp-lockups.patch]
    Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
    Signed-off-by: Ingo Molnar <mingo@elte.hu>

    diff -puN arch/i386/kernel/tsc.c~gtod-mark-tsc-unusable-for-highres-timers arch/i386/kernel/tsc.c
    --- a/arch/i386/kernel/tsc.c~gtod-mark-tsc-unusable-for-highres-timers
    +++ a/arch/i386/kernel/tsc.c
    @@ -459,10 +459,23 @@ static int __init init_tsc_clocksource(v
    current_tsc_khz = tsc_khz;
    clocksource_tsc.mult = clocksource_khz2mult(current_tsc_khz,
    clocksource_tsc.shift);
    +#ifndef CONFIG_HIGH_RES_TIMERS
    /* lower the rating if we already know its unstable: */
    if (check_tsc_unstable())
    clocksource_tsc.rating = 0;
    -
    +#else
    + /*
    + * Mark TSC unsuitable for high resolution timers. TSC has so
    + * many pitfalls: frequency changes, stop in idle ... When we
    + * switch to high resolution mode we can not longer detect a
    + * firmware caused frequency change, as the emulated tick uses
    + * TSC as reference. This results in a circular dependency.
    + * Switch only to high resolution mode, if pm_timer or such
    + * is available.
    + */
    + clocksource_tsc.rating = 50;
    + clocksource_tsc.is_continuous = 0;
    +#endif
    init_timer(&verify_tsc_freq_timer);
    verify_tsc_freq_timer.function = verify_tsc_freq;
    verify_tsc_freq_timer.expires =
    _
    --

    -
    To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    the body of a message to majordomo@vger.kernel.org
    More majordomo info at http://vger.kernel.org/majordomo-info.html
    Please read the FAQ at http://www.tux.org/lkml/

    \
     
     \ /
      Last update: 2006-11-10 00:49    [W:0.124 / U:60.644 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site