Clock Skew Due to CPU Frequency Management? (was Re: Dual-core system will not create NTP peers)
I had a very kind private communication from a list member. Let me
reformulate my question.
On the AMD64 dual-core platform, the system clock has far too much drift
even though the hardware clock seems well behaved. I don't seem to be
experiencing the "double-speed clock" problem that I see references to
on the net as of a few years ago, but I am experiencing some other odd
behavior. The most likely culprit, as far as I can tell from research,
is some interaction between the hardware's ability to adjust CPU clock
speed to save power/control temperature (which then influences the
system clock's theory of what a CPU tick means in terms of actual time
passing) with the dual-core mode.
But that seems rather wacky. I find it hard to believe that a kernel
release wouldn't work on dual core CPUs.
But if the problem really is that's the case, I would like to know what
boot-time settings I can use to test this hypothesis. For that matter
I'd like to know why the kernel itself isn't picking up on this
theoretical problem -- ISTR reading about an "enhanced" CPU clock mode
that could solve this problem, but I can't find references to it or how
to build a kernel or modules from source that would include this capability.
I've spent a substantial amount of time on this problem, and I can't
come to any conclusion. I have to wonder if it's a problem with NTP
itself, but if so it's a problem that only manifests itself on the AMD64
box, although I continue to fiddle with NTP settings.
--
Moshe Yudkowsky * moshe@pobox.com * www.pobox.com/~moshe
"If, after hearing my songs, just one human being is inspired to
say something nasty to a friend, it will all have been worthwhile."
-- Tom Lehrer
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