diff options
author | Jack Steiner <steiner@sgi.com> | 2007-01-11 01:52:44 +0100 |
---|---|---|
committer | Andi Kleen <andi@basil.nowhere.org> | 2007-01-11 01:52:44 +0100 |
commit | ed5316d4457b35c7b4942af028d6b878174264f7 (patch) | |
tree | ebaa1e04b31be2ae81d18411fa8ff41a2ed817f5 | |
parent | 9d24a81e84cee7cbf4656d178842838ac5ab23a4 (diff) | |
download | linux-ed5316d4457b35c7b4942af028d6b878174264f7.tar.bz2 |
[PATCH] x86-64: - Ignore long SMI interrupts in clock calibration
Ensure that no SMI interrupts occur between the read of the HPET & TSC
in the clock calibration loop.
I noticed that a 2.66GHz system incorrectly detected the processor
clock speed about 1/7 of the time:
time.c: Detected 2660.005 MHz processor. (most of the time)
time.c: Detected 2988.203 MHz processor. (sometime)
The problem is caused by an SMI interrupt occuring in hpet_calibrate_tsc()
between the read of the HPET & TSC. Prior to switching the BIOS into
ACPI mode, it appears that every 27msec an SMI interrupt occurs. The
SMI interrupt takes 4.8 msec to process.
Note: On my test system, TICK_MIN had to be >380. I picked 5000
to minimize risk of having a value that is too small for other
platforms.
Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andi Kleen <ak@suse.de>
arch/x86_64/kernel/time.c | 25 +++++++++++++++++++++----
1 file changed, 21 insertions(+), 4 deletions(-)
-rw-r--r-- | arch/x86_64/kernel/time.c | 25 |
1 files changed, 21 insertions, 4 deletions
diff --git a/arch/x86_64/kernel/time.c b/arch/x86_64/kernel/time.c index 9f05bc9b2dad..5cc76d0d331f 100644 --- a/arch/x86_64/kernel/time.c +++ b/arch/x86_64/kernel/time.c @@ -656,6 +656,25 @@ core_initcall(cpufreq_tsc); */ #define TICK_COUNT 100000000 +#define TICK_MIN 5000 + +/* + * Some platforms take periodic SMI interrupts with 5ms duration. Make sure none + * occurs between the reads of the hpet & TSC. + */ +static void __init read_hpet_tsc(int *hpet, int *tsc) +{ + int tsc1, tsc2, hpet1; + + do { + tsc1 = get_cycles_sync(); + hpet1 = hpet_readl(HPET_COUNTER); + tsc2 = get_cycles_sync(); + } while (tsc2 - tsc1 > TICK_MIN); + *hpet = hpet1; + *tsc = tsc2; +} + static unsigned int __init hpet_calibrate_tsc(void) { @@ -666,13 +685,11 @@ static unsigned int __init hpet_calibrate_tsc(void) local_irq_save(flags); local_irq_disable(); - hpet_start = hpet_readl(HPET_COUNTER); - rdtscl(tsc_start); + read_hpet_tsc(&hpet_start, &tsc_start); do { local_irq_disable(); - hpet_now = hpet_readl(HPET_COUNTER); - tsc_now = get_cycles_sync(); + read_hpet_tsc(&hpet_now, &tsc_now); local_irq_restore(flags); } while ((tsc_now - tsc_start) < TICK_COUNT && (hpet_now - hpet_start) < TICK_COUNT); |