From 3f4a0b917ce72ef47e438d354c433eb645218e87 Mon Sep 17 00:00:00 2001 From: john stultz Date: Tue, 17 Oct 2006 00:09:32 -0700 Subject: [PATCH] [PATCH] i386 Time: Avoid PIT SMP lockups Avoid possible PIT livelock issues seen on SMP systems (and reported by Andi), by not allowing it as a clocksource on SMP boxes. However, since the PIT may no longer be present, we have to properly handle the cases where SMP systems have TSC skew and fall back from the TSC. Since the PIT isn't there, it would "fall back" to the TSC again. So this changes the jiffies rating to 1, and the TSC-bad rating value to 0. Thus you will get the following behavior priority on i386 systems: tsc [if present & stable] hpet [if present] cyclone [if present] acpi_pm [if present] pit [if UP] jiffies Rather then the current more complicated: tsc [if present & stable] hpet [if present] cyclone [if present] acpi_pm [if present] pit [if cpus < 4] tsc [if present & unstable] jiffies Signed-off-by: John Stultz Cc: Andi Kleen Cc: Ingo Molnar Cc: Thomas Gleixner Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds --- arch/i386/kernel/i8253.c | 2 +- arch/i386/kernel/tsc.c | 6 +++--- kernel/time/jiffies.c | 2 +- 3 files changed, 5 insertions(+), 5 deletions(-) diff --git a/arch/i386/kernel/i8253.c b/arch/i386/kernel/i8253.c index 477b24daff..9a0060b92e 100644 --- a/arch/i386/kernel/i8253.c +++ b/arch/i386/kernel/i8253.c @@ -109,7 +109,7 @@ static struct clocksource clocksource_pit = { static int __init init_pit_clocksource(void) { - if (num_possible_cpus() > 4) /* PIT does not scale! */ + if (num_possible_cpus() > 1) /* PIT does not scale! */ return 0; clocksource_pit.mult = clocksource_hz2mult(CLOCK_TICK_RATE, 20); diff --git a/arch/i386/kernel/tsc.c b/arch/i386/kernel/tsc.c index b8fa0a8b2e..fbc95828cd 100644 --- a/arch/i386/kernel/tsc.c +++ b/arch/i386/kernel/tsc.c @@ -349,8 +349,8 @@ static int tsc_update_callback(void) int change = 0; /* check to see if we should switch to the safe clocksource: */ - if (clocksource_tsc.rating != 50 && check_tsc_unstable()) { - clocksource_tsc.rating = 50; + if (clocksource_tsc.rating != 0 && check_tsc_unstable()) { + clocksource_tsc.rating = 0; clocksource_reselect(); change = 1; } @@ -461,7 +461,7 @@ static int __init init_tsc_clocksource(void) clocksource_tsc.shift); /* lower the rating if we already know its unstable: */ if (check_tsc_unstable()) - clocksource_tsc.rating = 50; + clocksource_tsc.rating = 0; init_timer(&verify_tsc_freq_timer); verify_tsc_freq_timer.function = verify_tsc_freq; diff --git a/kernel/time/jiffies.c b/kernel/time/jiffies.c index 126bb30c4a..a99b2a6e6a 100644 --- a/kernel/time/jiffies.c +++ b/kernel/time/jiffies.c @@ -57,7 +57,7 @@ static cycle_t jiffies_read(void) struct clocksource clocksource_jiffies = { .name = "jiffies", - .rating = 0, /* lowest rating*/ + .rating = 1, /* lowest valid rating*/ .read = jiffies_read, .mask = 0xffffffff, /*32bits*/ .mult = NSEC_PER_JIFFY << JIFFIES_SHIFT, /* details above */ -- 2.39.5