x86: TSC make the calibration loop smarter

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The last changes made the calibration loop 250ms long which is far
too much. Try to do that more clever.

Experiments have shown that using a 10ms delay for the PIT based calibration
gives us a good enough value. If we have a reference (HPET/PMTIMER) and the
result of the PIT and the reference is close enough, then we can break out of
the calibration loop on a match right away and use the reference value.

Otherwise we just loop 3 times and decide then, which value to take.

One caveat is that for virtualized environments the PIT calibration often does
not work at all and I found out that 10us is a bit too short as well for the
reference to give a sane result. The solution here is to make the last loop
longer when the first two PIT calibrations failed.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

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Thomas Gleixner 2008-09-04 15:18:59 +00:00 • committed by Ingo Molnar

parent 827014be05

commit a977c40095

1 changed files with 58 additions and 37 deletions

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arch/x86/kernel/tsc.c

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