On Wed, 2014-04-30 at 14:56 +1000, Benjamin Herrenschmidt wrote:

On Wed, 2014-03-19 at 17:05 -0500, Scott Wood wrote:

quoted

On Wed, 2014-03-19 at 22:52 +0100, Christophe Leroy wrote:

quoted

This patch provides VIRT_CPU_ACCOUTING to PPC32 architecture.
Unlike PPC64, PPC32 doesn't provide the PACA register. Therefore the
implementation is similar to the one done in the IA64 architecture.
It is based on additional information added to the Task Info structure.

PACA isn't a register -- just a convention for how Linux uses a GPR.
Maybe it's time to use it on PPC32 as well?

PACA is actually a data structure and you really really don't want it
on ppc32 :-) Having a register point to current works, having a register
point to per-cpu data instead works too (ie, change what we do today),
but don't introduce a PACA *please* :-)

What is special about 64-bit that warrants doing things differently from
32-bit?

What is the difference between PACA and "per-cpu data", other than the
obscure name?
 
-Scott