diff options
Diffstat (limited to 'arch/x86/kernel/tsc.c')
| -rw-r--r-- | arch/x86/kernel/tsc.c | 14 |
1 files changed, 6 insertions, 8 deletions
diff --git a/arch/x86/kernel/tsc.c b/arch/x86/kernel/tsc.c index c0dd5b603749..a62c201c97ec 100644 --- a/arch/x86/kernel/tsc.c +++ b/arch/x86/kernel/tsc.c @@ -290,14 +290,15 @@ static inline int pit_verify_msb(unsigned char val) static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *deltap) { int count; - u64 tsc = 0; + u64 tsc = 0, prev_tsc = 0; for (count = 0; count < 50000; count++) { if (!pit_verify_msb(val)) break; + prev_tsc = tsc; tsc = get_cycles(); } - *deltap = get_cycles() - tsc; + *deltap = get_cycles() - prev_tsc; *tscp = tsc; /* @@ -311,9 +312,9 @@ static inline int pit_expect_msb(unsigned char val, u64 *tscp, unsigned long *de * How many MSB values do we want to see? We aim for * a maximum error rate of 500ppm (in practice the * real error is much smaller), but refuse to spend - * more than 25ms on it. + * more than 50ms on it. */ -#define MAX_QUICK_PIT_MS 25 +#define MAX_QUICK_PIT_MS 50 #define MAX_QUICK_PIT_ITERATIONS (MAX_QUICK_PIT_MS * PIT_TICK_RATE / 1000 / 256) static unsigned long quick_pit_calibrate(void) @@ -383,15 +384,12 @@ success: * * As a result, we can depend on there not being * any odd delays anywhere, and the TSC reads are - * reliable (within the error). We also adjust the - * delta to the middle of the error bars, just - * because it looks nicer. + * reliable (within the error). * * kHz = ticks / time-in-seconds / 1000; * kHz = (t2 - t1) / (I * 256 / PIT_TICK_RATE) / 1000 * kHz = ((t2 - t1) * PIT_TICK_RATE) / (I * 256 * 1000) */ - delta += (long)(d2 - d1)/2; delta *= PIT_TICK_RATE; do_div(delta, i*256*1000); printk("Fast TSC calibration using PIT\n"); |