Re: powerpc/64s: optimise syscall entry for virtual, relocatable case
From: Michael Ellerman <hidden>
Date: 2016-09-20 13:07:22
On Thu, 2016-15-09 at 09:03:21 UTC, Nicholas Piggin wrote:
The mflr r10 instruction was left over saving of lr when the code used lr to branch to system_call_entry from the exception handler. That was changed by 6a404806d to use the count register. The value is never used now, so mflr can be removed, and r10 can be used for storage rather than spilling to the SPR scratch register. The scratch register spill causes a long pipeline stall due to the SPR read after write. This change brings getppid syscall cost from 406 to 376 cycles on POWER8. getppid for non-relocatable case is 371 cycles. Signed-off-by: Nicholas Piggin <npiggin@gmail.com> Acked-by: Balbir Singh <bsingharora@gmail.com>
Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/18e3f56b1cacb96017e2a66844 cheers