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 <npig...@gmail.com> > Acked-by: Balbir Singh <bsinghar...@gmail.com>
Applied to powerpc next, thanks. https://git.kernel.org/powerpc/c/18e3f56b1cacb96017e2a66844 cheers