Andy Whitcroft <[email protected]> wrote:
>
> From: John Stultz <[email protected]>
>
> Suppress lost tick detection until we are fully initialised.
> This prevents any modifications to the high resolution timers
> from causing non-linearities in the flow of time. For example on
> an SMP system we resyncronise the TSC values for all processors.
> This results in a TSC reset which will be seen as a huge apparent
> tick loss. This can cause premature expiry of timers and in extreme
> cases can cause the soft lockup detection to fire.
>
> Acked-by: Andy Whitcroft <[email protected]>
>
> diff --git a/arch/i386/kernel/timers/timer_tsc.c b/arch/i386/kernel/timers/timer_tsc.c
> --- a/arch/i386/kernel/timers/timer_tsc.c
> +++ b/arch/i386/kernel/timers/timer_tsc.c
> @@ -45,6 +45,15 @@ static unsigned long last_tsc_high; /* m
> static unsigned long long monotonic_base;
> static seqlock_t monotonic_lock = SEQLOCK_UNLOCKED;
>
> +/* Avoid compensating for lost ticks before TSCs are synched */
> +static int detect_lost_ticks;
> +static int __init start_lost_tick_compensation(void)
> +{
> + detect_lost_ticks = 1;
> + return 0;
> +}
> +late_initcall(start_lost_tick_compensation);
> +
> /* convert from cycles(64bits) => nanoseconds (64bits)
> * basic equation:
> * ns = cycles / (freq / ns_per_sec)
> @@ -196,7 +205,8 @@ static void mark_offset_tsc_hpet(void)
>
> /* lost tick compensation */
> offset = hpet_readl(HPET_T0_CMP) - hpet_tick;
> - if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))) {
> + if (unlikely(((offset - hpet_last) > hpet_tick) && (hpet_last != 0))
> + && detect_lost_ticks) {
Simple enough. John, so you feel that this is 2.6.16 material?
Note that the time changes in -mm will blow this change away, so I'd be
needing a fresh version of this patch against next-mm, please.
-
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