powerpc/64s: exception optimise MSR handling

[Michael Ellerman]

On Thu, 2016-15-09 at 09:04:46 UTC, Nicholas Piggin wrote:
> mtmsrd with L=1 only affects MSR_EE and MSR_RI bits, and we always
> know what state those bits are, so the kernel MSR does not need to be
> loaded when modifying them.
> 
> mtmsrd is often in the critical execution path, so avoiding dependency
> on even L1 load is noticable. On a POWER8 this saves about 3 cycles
> from the syscall path, and possibly a few from other exception returns
> (not measured).
> 
> Signed-off-by: Nicholas Piggin <npiggin at gmail.com>

Applied to powerpc next, thanks.

https://git.kernel.org/powerpc/c/49d09bf2a66f4b5a6eabefb0d4

cheers