From 1be396794897f80bfc8774719ba60309a9e3d374 Mon Sep 17 00:00:00 2001 From: Martin Schwidefsky Date: Fri, 14 Aug 2009 15:47:20 +0200 Subject: [PATCH] timekeeping: Move reset of cycle_last for tsc clocksource to tsc 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 after a resume. The reason is that the TSC read function uses cycle_last to detect backwards going TSCs. In the resume case cycle_last contains the TSC value from the last update before the suspend. On resume the TSC starts counting from 0 again and would trip over the cycle_last comparison. This is subtle and surprising. Move the reset to a resume function in the tsc code. Signed-off-by: Martin Schwidefsky Acked-by: Thomas Gleixner Acked-by: John Stultz Cc: Daniel Walker LKML-Reference: <20090814134808.142191175@de.ibm.com> Signed-off-by: Thomas Gleixner --- arch/x86/kernel/tsc.c | 6 ++++++ kernel/time/timekeeping.c | 1 - 2 files changed, 6 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index 71f4368b357e..968425422c46 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -744,10 +744,16 @@ static cycle_t __vsyscall_fn vread_tsc(void) } #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 | diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 016a2591d719..b5673016089f 100644 --- a/kernel/time/timekeeping.c +++ b/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;