RFC: Performance Monitor Counters device

[Benjamin Herrenschmidt]

>Benjamin Herrenschmidt wrote:
>> Hrm... you should check the various CPU erratas, I think
>> the perf. counter exception suffers from the same bugs
>> the thermal exceptions has regarding clashing with DEC
>> and thus losing exception context information on some
>> G4s. If this is the case, that would basically prevent
>> using it.
>
>Ooh, that sounds bad!  Thanks for the hint.

Yah, and we have to thank MOL for helping us find out
what was going on with the TAU exception easily ;)

The way MOL plays with the DEC made the clash happen
more often, and since it then happened within MOL emulation
context, the MOL kernel module could figure out something
wrong happened, kill the emulator, and stay alive while
printing nice debug informations ;)
If that happened during normal kernel operations, I suspect
we would have just died hard.

Ben.


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