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.Received on Fri Oct 28 2005 - 12:26:26 UTC
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