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linux/arch/powerpc/lib/memcmp_64.S

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powerpc: Add 64bit optimised memcmp I noticed ksm spending quite a lot of time in memcmp on a large KVM box. The current memcmp loop is very unoptimised - byte at a time compares with no loop unrolling. We can do much much better. Optimise the loop in a few ways: - Unroll the byte at a time loop - For large (at least 32 byte) comparisons that are also 8 byte aligned, use an unrolled modulo scheduled loop using 8 byte loads. This is similar to our glibc memcmp. A simple microbenchmark testing 10000000 iterations of an 8192 byte memcmp was used to measure the performance: baseline: 29.93 s modified: 1.70 s Just over 17x faster. v2: Incorporated some suggestions from Segher: - Use andi. instead of rdlicl. - Convert bdnzt eq, to bdnz. It's just duplicating the earlier compare and was a relic from a previous version. - Don't use cr5, we have plans to use that CR field for fast local atomics. Signed-off-by: Anton Blanchard <anton@samba.org> Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
2015-01-21 01:27:38 +00:00
/*
* Author: Anton Blanchard <anton@au.ibm.com>
* Copyright 2015 IBM Corporation.
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version
* 2 of the License, or (at your option) any later version.
*/
#include <asm/ppc_asm.h>
#define off8 r6
#define off16 r7
#define off24 r8
#define rA r9
#define rB r10
#define rC r11
#define rD r27
#define rE r28
#define rF r29
#define rG r30
#define rH r31
#ifdef __LITTLE_ENDIAN__
#define LD ldbrx
#else
#define LD ldx
#endif
_GLOBAL(memcmp)
cmpdi cr1,r5,0
/* Use the short loop if both strings are not 8B aligned */
or r6,r3,r4
andi. r6,r6,7
/* Use the short loop if length is less than 32B */
cmpdi cr6,r5,31
beq cr1,.Lzero
bne .Lshort
bgt cr6,.Llong
.Lshort:
mtctr r5
1: lbz rA,0(r3)
lbz rB,0(r4)
subf. rC,rB,rA
bne .Lnon_zero
bdz .Lzero
lbz rA,1(r3)
lbz rB,1(r4)
subf. rC,rB,rA
bne .Lnon_zero
bdz .Lzero
lbz rA,2(r3)
lbz rB,2(r4)
subf. rC,rB,rA
bne .Lnon_zero
bdz .Lzero
lbz rA,3(r3)
lbz rB,3(r4)
subf. rC,rB,rA
bne .Lnon_zero
addi r3,r3,4
addi r4,r4,4
bdnz 1b
.Lzero:
li r3,0
blr
.Lnon_zero:
mr r3,rC
blr
.Llong:
li off8,8
li off16,16
li off24,24
std r31,-8(r1)
std r30,-16(r1)
std r29,-24(r1)
std r28,-32(r1)
std r27,-40(r1)
srdi r0,r5,5
mtctr r0
andi. r5,r5,31
LD rA,0,r3
LD rB,0,r4
LD rC,off8,r3
LD rD,off8,r4
LD rE,off16,r3
LD rF,off16,r4
LD rG,off24,r3
LD rH,off24,r4
cmpld cr0,rA,rB
addi r3,r3,32
addi r4,r4,32
bdz .Lfirst32
LD rA,0,r3
LD rB,0,r4
cmpld cr1,rC,rD
LD rC,off8,r3
LD rD,off8,r4
cmpld cr6,rE,rF
LD rE,off16,r3
LD rF,off16,r4
cmpld cr7,rG,rH
bne cr0,.LcmpAB
LD rG,off24,r3
LD rH,off24,r4
cmpld cr0,rA,rB
bne cr1,.LcmpCD
addi r3,r3,32
addi r4,r4,32
bdz .Lsecond32
.balign 16
1: LD rA,0,r3
LD rB,0,r4
cmpld cr1,rC,rD
bne cr6,.LcmpEF
LD rC,off8,r3
LD rD,off8,r4
cmpld cr6,rE,rF
bne cr7,.LcmpGH
LD rE,off16,r3
LD rF,off16,r4
cmpld cr7,rG,rH
bne cr0,.LcmpAB
LD rG,off24,r3
LD rH,off24,r4
cmpld cr0,rA,rB
bne cr1,.LcmpCD
addi r3,r3,32
addi r4,r4,32
bdnz 1b
.Lsecond32:
cmpld cr1,rC,rD
bne cr6,.LcmpEF
cmpld cr6,rE,rF
bne cr7,.LcmpGH
cmpld cr7,rG,rH
bne cr0,.LcmpAB
bne cr1,.LcmpCD
bne cr6,.LcmpEF
bne cr7,.LcmpGH
.Ltail:
ld r31,-8(r1)
ld r30,-16(r1)
ld r29,-24(r1)
ld r28,-32(r1)
ld r27,-40(r1)
cmpdi r5,0
beq .Lzero
b .Lshort
.Lfirst32:
cmpld cr1,rC,rD
cmpld cr6,rE,rF
cmpld cr7,rG,rH
bne cr0,.LcmpAB
bne cr1,.LcmpCD
bne cr6,.LcmpEF
bne cr7,.LcmpGH
b .Ltail
.LcmpAB:
li r3,1
bgt cr0,.Lout
li r3,-1
b .Lout
.LcmpCD:
li r3,1
bgt cr1,.Lout
li r3,-1
b .Lout
.LcmpEF:
li r3,1
bgt cr6,.Lout
li r3,-1
b .Lout
.LcmpGH:
li r3,1
bgt cr7,.Lout
li r3,-1
.Lout:
ld r31,-8(r1)
ld r30,-16(r1)
ld r29,-24(r1)
ld r28,-32(r1)
ld r27,-40(r1)
blr
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