15c2d45d17
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>
234 lines
2.8 KiB
ArmAsm
234 lines
2.8 KiB
ArmAsm
/*
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* Author: Anton Blanchard <anton@au.ibm.com>
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* Copyright 2015 IBM Corporation.
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*
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* This program is free software; you can redistribute it and/or
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* modify it under the terms of the GNU General Public License
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* as published by the Free Software Foundation; either version
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* 2 of the License, or (at your option) any later version.
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*/
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#include <asm/ppc_asm.h>
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#define off8 r6
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#define off16 r7
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#define off24 r8
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#define rA r9
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#define rB r10
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#define rC r11
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#define rD r27
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#define rE r28
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#define rF r29
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#define rG r30
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#define rH r31
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#ifdef __LITTLE_ENDIAN__
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#define LD ldbrx
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#else
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#define LD ldx
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#endif
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_GLOBAL(memcmp)
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cmpdi cr1,r5,0
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/* Use the short loop if both strings are not 8B aligned */
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or r6,r3,r4
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andi. r6,r6,7
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/* Use the short loop if length is less than 32B */
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cmpdi cr6,r5,31
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beq cr1,.Lzero
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bne .Lshort
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bgt cr6,.Llong
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.Lshort:
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mtctr r5
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1: lbz rA,0(r3)
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lbz rB,0(r4)
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subf. rC,rB,rA
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bne .Lnon_zero
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bdz .Lzero
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lbz rA,1(r3)
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lbz rB,1(r4)
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subf. rC,rB,rA
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bne .Lnon_zero
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bdz .Lzero
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lbz rA,2(r3)
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lbz rB,2(r4)
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subf. rC,rB,rA
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bne .Lnon_zero
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bdz .Lzero
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lbz rA,3(r3)
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lbz rB,3(r4)
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subf. rC,rB,rA
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bne .Lnon_zero
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addi r3,r3,4
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addi r4,r4,4
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bdnz 1b
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.Lzero:
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li r3,0
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blr
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.Lnon_zero:
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mr r3,rC
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blr
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.Llong:
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li off8,8
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li off16,16
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li off24,24
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std r31,-8(r1)
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std r30,-16(r1)
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std r29,-24(r1)
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std r28,-32(r1)
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std r27,-40(r1)
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srdi r0,r5,5
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mtctr r0
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andi. r5,r5,31
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LD rA,0,r3
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LD rB,0,r4
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LD rC,off8,r3
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LD rD,off8,r4
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LD rE,off16,r3
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LD rF,off16,r4
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LD rG,off24,r3
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LD rH,off24,r4
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cmpld cr0,rA,rB
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addi r3,r3,32
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addi r4,r4,32
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bdz .Lfirst32
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LD rA,0,r3
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LD rB,0,r4
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cmpld cr1,rC,rD
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LD rC,off8,r3
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LD rD,off8,r4
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cmpld cr6,rE,rF
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LD rE,off16,r3
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LD rF,off16,r4
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cmpld cr7,rG,rH
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bne cr0,.LcmpAB
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LD rG,off24,r3
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LD rH,off24,r4
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cmpld cr0,rA,rB
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bne cr1,.LcmpCD
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addi r3,r3,32
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addi r4,r4,32
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bdz .Lsecond32
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.balign 16
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1: LD rA,0,r3
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LD rB,0,r4
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cmpld cr1,rC,rD
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bne cr6,.LcmpEF
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LD rC,off8,r3
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LD rD,off8,r4
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cmpld cr6,rE,rF
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bne cr7,.LcmpGH
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LD rE,off16,r3
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LD rF,off16,r4
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cmpld cr7,rG,rH
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bne cr0,.LcmpAB
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LD rG,off24,r3
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LD rH,off24,r4
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cmpld cr0,rA,rB
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bne cr1,.LcmpCD
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addi r3,r3,32
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addi r4,r4,32
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bdnz 1b
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.Lsecond32:
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cmpld cr1,rC,rD
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bne cr6,.LcmpEF
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cmpld cr6,rE,rF
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bne cr7,.LcmpGH
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cmpld cr7,rG,rH
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bne cr0,.LcmpAB
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bne cr1,.LcmpCD
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bne cr6,.LcmpEF
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bne cr7,.LcmpGH
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.Ltail:
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ld r31,-8(r1)
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ld r30,-16(r1)
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ld r29,-24(r1)
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ld r28,-32(r1)
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ld r27,-40(r1)
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cmpdi r5,0
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beq .Lzero
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b .Lshort
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.Lfirst32:
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cmpld cr1,rC,rD
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cmpld cr6,rE,rF
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cmpld cr7,rG,rH
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bne cr0,.LcmpAB
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bne cr1,.LcmpCD
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bne cr6,.LcmpEF
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bne cr7,.LcmpGH
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b .Ltail
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.LcmpAB:
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li r3,1
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bgt cr0,.Lout
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li r3,-1
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b .Lout
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.LcmpCD:
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li r3,1
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bgt cr1,.Lout
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li r3,-1
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b .Lout
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.LcmpEF:
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li r3,1
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bgt cr6,.Lout
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li r3,-1
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b .Lout
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.LcmpGH:
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li r3,1
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bgt cr7,.Lout
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li r3,-1
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.Lout:
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ld r31,-8(r1)
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ld r30,-16(r1)
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ld r29,-24(r1)
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ld r28,-32(r1)
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ld r27,-40(r1)
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blr
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