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authorJack Steiner <steiner@sgi.com>2007-01-11 01:52:44 +0100
committerAndi Kleen <andi@basil.nowhere.org>2007-01-11 01:52:44 +0100
commited5316d4457b35c7b4942af028d6b878174264f7 (patch)
treeebaa1e04b31be2ae81d18411fa8ff41a2ed817f5 /arch/x86_64
parent9d24a81e84cee7cbf4656d178842838ac5ab23a4 (diff)
downloadlinux-linaro-stable-ed5316d4457b35c7b4942af028d6b878174264f7.tar.gz
[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(-)
Diffstat (limited to 'arch/x86_64')
-rw-r--r--arch/x86_64/kernel/time.c25
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);