Messages in this thread | | | Date | Mon, 10 Mar 2014 11:39:44 +0100 (CET) | From | Thomas Gleixner <> | Subject | Re: [RESEND] Fast TSC calibration fails with v3.14-rc1 and later |
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On Mon, 10 Mar 2014, Julian Wollrath wrote: > on a Thinkpad x121e (AMD E-450 APU) with version 3.13.5 and earlier of > the kernel I get: > [...] > [ 0.000000] tsc: Fast TSC calibration using PIT > [ 0.001000] tsc: Detected 1646.619 MHz processor > [ 0.000004] Calibrating delay loop (skipped), value calculated using > timer frequency.. 3293.23 BogoMIPS (lpj=1646619) > [...] > > > but starting with v3.14-rc1 the fast TSC calibration fails: > [...] > [ 0.000000] tsc: Fast TSC calibration failed > [ 0.000000] tsc: PIT calibration matches HPET. 1 loops > [ 0.000000] tsc: Detected 1646.490 MHz processor > [...]
The only change in the calibration code post 3.13 is that we added the MSR based calibration for ATOM:
@@ -419,6 +651,13 @@ unsigned long native_calibrate_tsc(void) unsigned long flags, latch, ms, fast_calibrate; int hpet = is_hpet_enabled(), i, loopmin;
+ /* Calibrate TSC using MSR for Intel Atom SoCs */ + local_irq_save(flags); + fast_calibrate = try_msr_calibrate_tsc(); + local_irq_restore(flags); + if (fast_calibrate) + return fast_calibrate; + local_irq_save(flags); fast_calibrate = quick_pit_calibrate(); local_irq_restore(flags);
And that definitely does not affect the quick calibration. No idea, except bisecting.
Thanks,
tglx
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