Re: powernow-k8 and stuck change-pending bit

[John Belmonte <john@neggie.net>]

Devriendt, Paul wrote:
>>symptoms:
>>
>>    After working fine for a while (several minutes to several hours),
>>cpufreq seems to get into a bad state where:
>>
>>     * change pending bit set / stuck kernel messages appear
>>
>>     * reloading powernow-k8 module fails, with "change 
>>pending bit stuck"
> 
[...]
> The most likely scenario here is the VRM was unable to change
> voltage, and that means flaky hardware as it has previously been
> able to successfully do so. The reason I pick on the VRM and not
> some sort of issue with the HyperTransport fabric is that it is
> unlikely anything would still be alive if there was some sort of 
> problem coming back from the LDT_STOP.
> 
> Assuming the VRM continues to supply the current voltage within 
> spec, the system will stay up indefinitely, at the current
> voltage and frequency.
> 
> The best path to follow would be to investigate warrantee replacement
> of the board.

Thanks for the info Paul.  I've had the motherboard replaced with an
identical model.  This new board seems to have the same problem, except
that when a transition finally fails, Linux hangs bad enough to require
a hard reset of the system.

With two boards having this problem, it suggests either a bad
motherboard design or some bad interaction between Linux and the
motherboard.  (It seems strange that the manufacturer wouldn't have seen
this problem under Windows.)  Much less likely is that I have a bad CPU.

--John