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Message-Id: <67cf476f657e87b2ea586951a57ae3ba3c1e3c0c.1435655733.git.christophe.leroy@c-s.fr> Date: Wed, 5 Aug 2015 15:29:35 +0200 (CEST) From: Christophe Leroy <christophe.leroy@....fr> To: Benjamin Herrenschmidt <benh@...nel.crashing.org>, Paul Mackerras <paulus@...ba.org>, Michael Ellerman <mpe@...erman.id.au>, scottwood@...escale.com Cc: linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org, Joakim Tjernlund <joakim.tjernlund@...nsmode.se> Subject: [PATCH v2 2/2] powerpc32: optimise csum_partial() loop On the 8xx, load latency is 2 cycles and taking branches also takes 2 cycles. So let's unroll the loop. Signed-off-by: Christophe Leroy <christophe.leroy@....fr> --- v2: Only use lwzu for the last load as lwzu has undocumented additional latency arch/powerpc/lib/checksum_32.S | 16 +++++++++++++++- 1 file changed, 15 insertions(+), 1 deletion(-) diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S index 2e4879c..9c48ee0 100644 --- a/arch/powerpc/lib/checksum_32.S +++ b/arch/powerpc/lib/checksum_32.S @@ -75,10 +75,24 @@ _GLOBAL(csum_partial) srwi. r6,r4,2 /* # words to do */ adde r5,r5,r0 beq 3f -1: mtctr r6 +1: andi. r6,r6,3 /* Prepare to handle words 4 by 4 */ + beq 21f + mtctr r6 2: lwzu r0,4(r3) adde r5,r5,r0 bdnz 2b +21: srwi. r6,r4,4 /* # blocks of 4 words to do */ + beq 3f + mtctr r6 +22: lwz r0,4(r3) + lwz r6,8(r3) + lwz r7,12(r3) + lwzu r8,16(r3) + adde r5,r5,r0 + adde r5,r5,r6 + adde r5,r5,r7 + adde r5,r5,r8 + bdnz 22b 3: andi. r0,r4,2 beq+ 4f lhz r0,4(r3) -- 2.1.0 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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