From: Martin Schwidefsky change_clocksource resets the cycle_last value to zero then sets it to a value read from the clocksource. The reset to zero is required only for the TSC clocksource to make the read_tsc function work. This is subtle and surprising. Move the reset to a resume function in the tsc code. Cc: Ingo Molnar Cc: Daniel Walker Cc: John Stultz Acked-by: Thomas Gleixner Signed-off-by: Martin Schwidefsky --- arch/x86/kernel/tsc.c | 6 ++++++ kernel/time/timekeeping.c | 1 - 2 files changed, 6 insertions(+), 1 deletion(-) Index: linux-2.6/arch/x86/kernel/tsc.c =================================================================== --- linux-2.6.orig/arch/x86/kernel/tsc.c +++ linux-2.6/arch/x86/kernel/tsc.c @@ -744,10 +744,16 @@ static cycle_t __vsyscall_fn vread_tsc(v } #endif +static void resume_tsc(void) +{ + clocksource_tsc.cycle_last = 0; +} + static struct clocksource clocksource_tsc = { .name = "tsc", .rating = 300, .read = read_tsc, + .resume = resume_tsc, .mask = CLOCKSOURCE_MASK(64), .shift = 22, .flags = CLOCK_SOURCE_IS_CONTINUOUS | Index: linux-2.6/kernel/time/timekeeping.c =================================================================== --- linux-2.6.orig/kernel/time/timekeeping.c +++ linux-2.6/kernel/time/timekeeping.c @@ -295,7 +295,6 @@ static void change_clocksource(void) if (old->disable) old->disable(old); - clock->cycle_last = 0; clock->cycle_last = clock->read(clock); clock->error = 0; clock->xtime_nsec = 0; -- blue skies, Martin. "Reality continues to ruin my life." - Calvin. -- 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/