[PATCH 5/8] cell: enable pause(0) in cpu_idle

[Segher Boessenkool]

>> Does your cpu support very_low?  Can it be disabled without disabling
>> low?   If not, only one of these is needed.   The generic has both
>> because some older cpus did not have very_low.  This code results in a
>> periodic bump up to low on cpus that support both.
>>
>> And you set HMT_low in pauze_zero.
>
> Hmm, I wonder if that might be one of the causes of the performance 
> problems
> we see on DD2 hardware (which can't do pauze_zero). Toggling between 
> HMT_low
> and HMT_very_low on one thread might cause problems in the pipeline 
> for the
> other thread in theory.
> Which document would be the one telling me if HMT_very_low is 
> supported?

CBEA claims to be compatible with the PowerPC 2.02 arch, which defines
"very low" -- although it only says "it provides a hint to the 
processor",
so your CPU might very well just ignore it.

I grepped and grepped, but couldn't find anything about the thread 
priority
in any of the Cell docs (except for lots of stuff relating to the 
interrupt
controller ;-) )

You'll just have to experiment I guess (or ask the chip guys...)


Segher