On PPC_8xx, lwz has a 2 cycles latency, and branching also takes 2 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.le...@c-s.fr>
---
arch/powerpc/lib/checksum_32.S | 10 +++++++---
1 file changed, 7 insertions(+), 3 deletions(-)
diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S
index 6d67e05..5500704 100644
--- a/arch/powerpc/lib/checksum_32.S
+++ b/arch/powerpc/lib/checksum_32.S
@@ -26,13 +26,17 @@
_GLOBAL(ip_fast_csum)
lwz r0,0(r3)
lwzu r5,4(r3)
- addic. r4,r4,-2
+ addic. r4,r4,-4
addc r0,r0,r5
mtctr r4
blelr-
-1: lwzu r4,4(r3)
- adde r0,r0,r4
+ lwzu r5,4(r3)
+ lwzu r4,4(r3)
+ adde r0,r0,r5
+1: adde r0,r0,r4
+ lwzu r4,4(r3)
bdnz 1b
+ adde r0,r0,r4
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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