TSC instead of ACPI: powerd doesn't work anymore (to be
expected?)
Poul-Henning Kamp
phk at phk.freebsd.dk
Fri Oct 28 07:26:26 PDT 2005
In message <43622BEF.3030006 at freebsd.org>, Colin Percival writes:
>Alexander Leidinger wrote:
>> Poul-Henning Kamp <phk at phk.freebsd.dk> wrote:
>>> In general, if you run powerd to change your cpu clock (= TSC
>>> frequency), using TSC as timecounter is _not_ what you want to do.
>>
>> Is it not possible to recalibrate on frequency change, or is it "just" that
>> nobody wrote the code do to it?
>
>It's not possible in any useful way. When power management code changes
>the TSC frequency, it doesn't change the frequency directly; instead, it
>sends a message to the CPU saying "please, if you feel like it, could you
>change your frequency to <foo> some time soon?"
>
>Even if you manage to handle the change in frequency, the timecounter
>would significantly lose accuracy due to not knowing exactly when the
>change in frequency occurred.
This is stuff you can calibrate your way out of given enough
time, effort and external reference, but a generic solution is
not possible.
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
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