Re: PATCH - update TSC freq when cpufreq changes it

Poul-Henning Kamp wrote:
In message <45E5D760.4030409@xxxxxxxx>, Nate Lawson writes:
Poul-Henning Kamp wrote:

It's a valid question, but mostly irrelevant.

Not at all. It may be a lot cheaper for us to just use the
value from the ACPI than to calibrate. Only in the increasingly
rare case where TSC is used for timecounter AND the system isn't
using NTP is the precise frequency really interesting.


Ah, that's something different. I don't think it's a good idea to use
the provided value outright when something more empirical is available.
With cpufreq modes like p4tcc or acpi_throttling, you only have a
relative setting anyway (i.e. 50%) so you still have to measure the base
freq at some point. Boot is a good place to do it.

Ultimately, my goal is to re-calibrate (with intr on) each level the
first time it's used, then cache it in cpufreq as the "real" freq. It
will provide that value in the cf_level struct and then eventhandler
consumers can use that. That value will be accurate and empirical. For
now, the goal is to just get TSC matching reality a little better (say
+/- 1% instead of +100% or so).

--
Nate
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