2007-05-21 15:43:40

by Joachim Deguara

Subject: [PATCH] -rt fix TSC calibration from PM Timer

The code to calibrate TSC frequency from the PM timer does not work on my
laptop with the 2.6.21-rt5.

[ 0.247815] time.c: Detected 62117.606 MHz processor.

The code looks to be copied from the calibration from HPET but unfortunately
it reports frequency instead of period in femtoseconds as the HPET does. I
also rearranged the math to make the femtoseconds and kHz clearer but it does
loose a negligible amount of precision.

Signed-off-by: Joachim Deguara <[email protected]>

Index: 2.6-rt/arch/x86_64/kernel/tsc.c
===================================================================
--- 2.6-rt.orig/arch/x86_64/kernel/tsc.c
+++ 2.6-rt/arch/x86_64/kernel/tsc.c
@@ -187,14 +187,14 @@ void __init tsc_calibrate(void)
return;
}

- tsc2 = (tsc2 - tsc1) * 1000000000L;
+ tsc2 = tsc2 - tsc1;

if (hpet) {
hpet2 = (hpet2 - hpet1) & 0xFFFFFFFF;
- tsc1 = (hpet2 * hpet_readl(HPET_PERIOD)) / 1000;
+ tsc1 = hpet2 * hpet_readl(HPET_PERIOD) / 1e12;
} else {
pm2 = (pm2 -pm1) & ACPI_PM_MASK;
- tsc1 = (pm2 * PMTMR_TICKS_PER_SEC) / 1000;
+ tsc1 = (pm2 * 1e3) / PMTMR_TICKS_PER_SEC;
}

tsc_khz = tsc2 / tsc1;

2007-05-21 15:54:37

by Thomas Gleixner

Subject: Re: [PATCH] -rt fix TSC calibration from PM Timer

On Mon, 2007-05-21 at 17:43 +0200, Joachim Deguara wrote:
> The code to calibrate TSC frequency from the PM timer does not work on my
> laptop with the 2.6.21-rt5.
>
> [ 0.247815] time.c: Detected 62117.606 MHz processor.

I know. The code was fixed in the x86_64-hrt queue, but never moved to
-rt. The sync to -hrt is already in the -rt6 pipeline.

tglx