Date: Fri, 09 Jun 2006 21:23:32 +0300 From: Andriy Gapon <avg@icyb.net.ua> To: freebsd-hackers@freebsd.org Subject: in-flight timer(s) recalibration Message-ID: <4489BCA4.5050909@icyb.net.ua>
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In-flight timer(s) recalibration - is it a good idea ? How to do it ? This question comes from the following: in 6.1 we use LAPIC timer even on UP systems; in scenarios where FSB frequency can be changed on the fly (this is not hypothetical) that results in bad time-keeping as LAPIC timer frequency is derived from FSB frequency. I'd like to be able to do something like what lapic_setup_clock() does, but through a proper interface and probably at smaller cost (I mean 2 second DELAY). I think that my need is pretty much LAPIC-timer centered because TSC should not be used in my case anyway and i8254 is mutually exclusive with LAPIC (at present, I think) and it is not affected by FSB frequency (is it?). BTW, maybe I will talk utter nonsense now, but is it possible to self-tune timer interrupt frequency by checking time elapsed between interrupts using the best available (or currently selected) timecounter ? -- Andriy Gapon
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