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SubjectRe: Linux 2.6.29-rc6


On Mon, 9 Mar 2009, Jesper Krogh wrote:
>
> First boot.
> [ 0.000000] ref_freq: 2311825 pit_freq: 2310386
> Second boot:
> [ 0.000000] ref_freq: 2311803 pit_freq: 2310190
> Third boot:
> [ 0.000000] ref_freq: 2311824 pit_freq: 2310080
> Fourth boot:
> [ 0.000000] ref_freq: 2311831 pit_freq: 2310130

It's really quite impressively stable, but the fast-PIT calibration
frequency is reliably about 3/4 of a promille low. Or, put another way,
the TSC difference over the pit calibration is just a _tad_ too small
compared to the value we'd expect if that loop of pit_expect_msb() would
really run at the expected delay of a 1.193182MHz clock divided by 256.

And it's stable in that it really always seems to be off by a very similar
amount. It's not moving around very much.

I also wonder why it seems to happen mainly just to _you_. There's
absolutely nothing odd in your system, neither a slow CPU or anything
else that would stand out.

Grr. Very annoyingly non-obvious.

Linus


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