Re: Linux 2.6.29-rc6

[Jesper Krogh]

Linus Torvalds wrote:
> Jesper, here's a patch that actually tries to take teh TSC error really 
> into account, and which I suspect will result (on your machine) in failing 
> the fast PIT calibration. 
>
> It also has a few extra printk's for debugging, and to see just what the 
> values are on your machine.
>
> The idea behind the patch is to just keep track of how big the difference 
> was in TSC values between two successive reads of the PIT timer. We only 
> really care about the difference when the MSB turns around, and we only 
> really care about the two end points. The maximum error in TSC estimation 
> will simply be the sum of the differences at those points (d1 and d2).
>
> We can then compare the maximum error with the actual TSC differences 
> between those points, and see if the max error is within 500 ppm. That 
> _should_ mean that it all works - assuming that the PIT itself is running 
> at the correct frequency, of course!
>
> Regardless of whether is succeeds or not, it will print out some debug 
> messages, which will be interesting to see.


[    0.000000] Fast TSC delta=34227730, error=6223+6219=12442
[    0.000000] Fast TSC calibration using PIT
[    0.000000] Detected 2312.045 MHz processor.

Using "ntpq -c peers" .. the offset steadily grows as time goes.

Full dmesg: http://krogh.cc/~jesper/dmesg-linux-2.6.29-rc8-linus1.txt

jk@quad11:~$ ntpdc -c kerninfo
pll offset:           0.085167 s
pll frequency:        -18.722 ppm
maximum error:        0.137231 s
estimated error:      0.008823 s
status:               0001  pll
pll time constant:    6
precision:            1e-06 s
frequency tolerance:  500 ppm



--
Jesper


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