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>

3 files changed, 237 insertions, 1 deletions

diff --git a/arch/powerpc/lib/Makefile b/arch/powerpc/lib/Makefile
index 1b01159b81f3..5526156aae5f 100644
--- a/arch/powerpc/lib/Makefile
+++ b/arch/powerpc/lib/Makefile
@@ -15,7 +15,8 @@ obj-$(CONFIG_PPC32)	+= div64.o copy_32.o
 
 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
diff --git a/arch/powerpc/lib/memcmp_64.S b/arch/powerpc/lib/memcmp_64.S
new file mode 100644
index 000000000000..8953d2382a65
--- /dev/null
+++ b/arch/powerpc/lib/memcmp_64.S
@@ -0,0 +1,233 @@
+/*
+ * 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
diff --git a/arch/powerpc/lib/string.S b/arch/powerpc/lib/string.S
index 1b5a0a09d609..c80fb49ce607 100644
--- a/arch/powerpc/lib/string.S
+++ b/arch/powerpc/lib/string.S
@@ -93,6 +93,7 @@ _GLOBAL(strlen)
         subf    r3,r3,r4
         blr
 
+#ifdef CONFIG_PPC32
 _GLOBAL(memcmp)
         PPC_LCMPI 0,r5,0
         beq-    2f
@@ -106,6 +107,7 @@ _GLOBAL(memcmp)
         blr
 2:      li      r3,0
         blr
+#endif
 
 _GLOBAL(memchr)
         PPC_LCMPI 0,r5,0