Re: [RFC/PATCH] Make powerpc64 use __thread for per-cpu variables

[David Howells <dhowells@redhat.com>]

Benjamin Herrenschmidt <benh@kernel.crashing.org> wrote:

> > That first cache line of current_thread_info() should be so hot that
> > it's probably just fine to use current_thread_info()->task since
> > you're just doing a mask on a fixed register (r1) to implement that.
> 
> Iirc, he tried that, though it did bloat the kernel size a bit due the
> the amount of occurences of current-> in there. We are now thinking
> about either dedicating a register to current (that would avoid the
> problem of printk() using it in start_kernel before we get the per-cpu
> areas setup) in addition to __thread (heh, we have lots of registers on
> ppc :) or maybe putting current back in the paca...

I dedicated registers to current and current threadinfo in the FRV arch.  As I
recall doing that improved both performance and code size quite a bit.  It also
means that I get sensible bug panic reports when the stack pointer overruns the
stack space.

David