Invert sense of SLB class bit

[Paul Mackerras]

Sonny Rao writes:

> So, when exactly do we go into real mode ?  I know the SLB handler is
> now run in real mode, but is anything else? 

On every interrupt and exception (including system calls); i.e. every
time we enter the kernel.  A few are handled entirely in real mode,
but for most we do a small amount of exception entry code and then do
an rfid instruction to turn the MMU back on.

> If we want to look at best-case improvements -- meaning a lot of SLB
> reloading and userspace context-switching, I suppose I should select a
> machine with a fair amount of memory.
> 
> Either way, I'm going to run SDET on a 2-way box w/ 8GB of RAM and see
> if I can find a difference.  If necessary, I'll find a bigger box to
> test on.

SDET sounds like a good choice, since it will do lots of system calls
as well as context switches.

Is this a POWER5 machine?

Paul.