The patch titled
i386 Time: Avoid PIT SMP lockups
has been added to the -mm tree. Its filename is
i386-time-avoid-pit-smp-lockups.patch
See http://www.zip.com.au/~akpm/linux/patches/stuff/added-to-mm.txt to find
out what to do about this
------------------------------------------------------
Subject: i386 Time: Avoid PIT SMP lockups
From: john stultz <johnstul@xxxxxxxxxx>
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 <johnstul@xxxxxxxxxx>
Cc: Andi Kleen <ak@xxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxx>
---
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 -puN arch/i386/kernel/i8253.c~i386-time-avoid-pit-smp-lockups arch/i386/kernel/i8253.c
--- a/arch/i386/kernel/i8253.c~i386-time-avoid-pit-smp-lockups
+++ a/arch/i386/kernel/i8253.c
@@ -109,7 +109,7 @@ static struct clocksource clocksource_pi
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 -puN arch/i386/kernel/tsc.c~i386-time-avoid-pit-smp-lockups arch/i386/kernel/tsc.c
--- a/arch/i386/kernel/tsc.c~i386-time-avoid-pit-smp-lockups
+++ a/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(v
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 -puN kernel/time/jiffies.c~i386-time-avoid-pit-smp-lockups kernel/time/jiffies.c
--- a/kernel/time/jiffies.c~i386-time-avoid-pit-smp-lockups
+++ a/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 */
_
Patches currently in -mm which might be from johnstul@xxxxxxxxxx are
i386-time-avoid-pit-smp-lockups.patch
posix-cpu-timers-prevent-signal-delivery-starvation.patch
gtod-exponential-update_wall_time.patch
gtod-persistent-clock-support-core.patch
gtod-persistent-clock-support-i386.patch
-
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