Messages in this thread Patch in this message | | | From | Christophe Leroy <> | Subject | [PATCH v2] powerpc32: rearrange instructions order in ip_fast_csum() | Date | Tue, 30 Jun 2015 15:51:28 +0200 (CEST) |
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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 <christophe.leroy@c-s.fr> --- arch/powerpc/lib/checksum_32.S | 11 +++++++---- 1 file changed, 7 insertions(+), 4 deletions(-)
diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S index 9c48ee0..6fbadfe 100644 --- a/arch/powerpc/lib/checksum_32.S +++ b/arch/powerpc/lib/checksum_32.S @@ -27,13 +27,16 @@ _GLOBAL(ip_fast_csum) lwz r0,0(r3) lwzu r5,4(r3) - addic. r4,r4,-2 + lwzu r6,4(r3) + lwzu r7,4(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
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