On PPC_8xx, lwz has a 2 cycles latency, and branching also takes 2 cycles. On some other powerpc, lwz has 3 cycles.
As the size of the header is minimum 5 words, we can unroll the loop for the first words to reduce number of branching, and we can re-order the instructions to limit loading latency. Signed-off-by: Christophe Leroy <[email protected]> --- v3: Only use lwzu for the last load as lwzu has undocumented additional latency arch/powerpc/lib/checksum_32.S | 13 ++++++++----- 1 file changed, 8 insertions(+), 5 deletions(-) diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S index 9c48ee0..3ef6e3f 100644 --- a/arch/powerpc/lib/checksum_32.S +++ b/arch/powerpc/lib/checksum_32.S @@ -26,14 +26,17 @@ */ _GLOBAL(ip_fast_csum) lwz r0,0(r3) - lwzu r5,4(r3) - addic. r4,r4,-2 + lwz r5,4(r3) + lwz r6,8(r3) + lwzu r7,12(r3) + addi r4,r4,-4 addc r0,r0,r5 mtctr r4 - blelr- -1: lwzu r4,4(r3) - adde r0,r0,r4 + adde r0,r0,r6 +1: adde r0,r0,r7 + lwzu r7,4(r3) bdnz 1b + adde r0,r0,r7 addze r0,r0 /* add in final carry */ rlwinm r3,r0,16,0,31 /* fold two halves together */ add r3,r0,r3 -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
