From 316da3b3fc8efa9a5d2c99e0d449f01ff38c6aba Mon Sep 17 00:00:00 2001 From: Thomas Gleixner Date: Wed, 30 Jan 2008 13:30:02 +0100 Subject: [PATCH] x86: restrict PIT clocksource usage PIT clocksource is registered unconditionally even when HPET is enabled or when PIT is replaced by the local APIC timer. In both cases PIT can not be used as it is stopped and the readout would be stale. Prevent registering PIT in those cases. patch depends on: x86: offer is_hpet_enabled() on !CONFIG_HPET_TIMER too Signed-off-by: Thomas Gleixner Signed-off-by: Ingo Molnar --- arch/x86/kernel/i8253.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-) diff --git a/arch/x86/kernel/i8253.c b/arch/x86/kernel/i8253.c index a42c8074532..0f8f35458a8 100644 --- a/arch/x86/kernel/i8253.c +++ b/arch/x86/kernel/i8253.c @@ -197,7 +197,15 @@ static struct clocksource clocksource_pit = { static int __init init_pit_clocksource(void) { - if (num_possible_cpus() > 1) /* PIT does not scale! */ + /* + * Several reasons not to register PIT as a clocksource: + * + * - On SMP PIT does not scale due to i8253_lock + * - when HPET is enabled + * - when local APIC timer is active (PIT is switched off) + */ + if (num_possible_cpus() > 1 || is_hpet_enabled() || + pit_clockevent.mode != CLOCK_EVT_MODE_PERIODIC) return 0; clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20);