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>
obj-$(CONFIG_PPC64) += copypage_64.o copyuser_64.o \
usercopy_64.o mem_64.o hweight_64.o \
- copyuser_power7.o string_64.o copypage_power7.o
+ copyuser_power7.o string_64.o copypage_power7.o \
+ memcmp_64.o
ifeq ($(CONFIG_GENERIC_CSUM),)
obj-y += checksum_$(CONFIG_WORD_SIZE).o
obj-$(CONFIG_PPC64) += checksum_wrappers_64.o
--- /dev/null
+/*
+ * 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
subf r3,r3,r4
blr
+#ifdef CONFIG_PPC32
_GLOBAL(memcmp)
PPC_LCMPI 0,r5,0
beq- 2f
blr
2: li r3,0
blr
+#endif
_GLOBAL(memchr)
PPC_LCMPI 0,r5,0
projects / cascardo / linux.git / commitdiff