time runs too slow on maple

[Benjamin Herrenschmidt]

On Mon, 2006-01-09 at 16:44 -0600, linas wrote:

> arch/powerpc/kernel/smp-tbsync.c:  smp_generic_give_timebase()
> 
> leads me to think that the maple board has a clock with a 
> huge amount of jitter, its bouncing all over the place.
> However, the smp_generic_give_timebase() isn't taking any 
> averages that would smooth out the jitter; instead, it locks
> onto some random value and uses that. 
> 
> I might be able to hack some averaging into that chunk of code, 
> but I don't know this stuff, not sure if that would be the right fix.

We don't know if the problem has anything to do with the SMP tbsync. You
are certainly welcome to improve that code, but the root of the problem
is probably that the timebase calibration that we obtain from Open
Firmware is not precise. Either that, or the clock is indeed not very
stable (that would be bad). The first one could be worked around by
doing some proper calibration and updating PIBS I suppose.

ben.