On an HP ze1115 notebook with a Mobile AMD K7, the CPU speed is measured twice, once when the CPU is initialized, and a second time when the powerrnow system is started. Sometimes the two readings agree; however, the second reading is usually higher, sometimes by very large factors. The dmesg excerpts below show one case where the difference is small.
Initializing CPU#0
PID hash table entries: 4096 (order: 12, 65536 bytes)
Detected 1100.134 MHz process
powernow: PowerNOW! Technology present. Can scale: frequency and voltage.
Detected 1148.044 MHz processor.
powernow: SGTC: 10000
powernow: Minimum speed 521 MHz. Maximum speed 1148 MHz.
The cpu frequency on this machine is measured using calibrate_tsc, which calls mach_countup between rdtsc calls. When the second speed determination is made, interrupts have been enabled, which makes the loop counter value in mach_count to be too small and the cpu frequency to be too high.
The two-line patch against 2.6.14 is shown below. With it, a second (faulty) determination of cpu_khz is avoided. BTW, this fix handles Bugzilla bugs #5266 and 5435.
Signed-off-by: Larry Finger <[email protected]>
---
diff --git a/arch/i386/kernel/time.c b/arch/i386/kernel/time.c
--- a/arch/i386/kernel/time.c
+++ b/arch/i386/kernel/time.c
@@ -78,7 +78,7 @@ u64 jiffies_64 = INITIAL_JIFFIES;
EXPORT_SYMBOL(jiffies_64);
-unsigned int cpu_khz; /* Detected as we calibrate the TSC */
+unsigned int cpu_khz=0; /* Detected as we calibrate the TSC */
EXPORT_SYMBOL(cpu_khz);
extern unsigned long wall_jiffies;
diff --git a/arch/i386/kernel/timers/common.c b/arch/i386/kernel/timers/common.c
--- a/arch/i386/kernel/timers/common.c
+++ b/arch/i386/kernel/timers/common.c
@@ -151,7 +151,7 @@ unsigned long read_timer_tsc(void)
/* calculate cpu_khz */
void init_cpu_khz(void)
{
- if (cpu_has_tsc) {
+ if (cpu_has_tsc && !cpu_khz) {
unsigned long tsc_quotient = calibrate_tsc();
if (tsc_quotient) {
/* report CPU clock rate in Hz.
-
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