Commit 2d9ee327 authored by Simon Guo's avatar Simon Guo Committed by Michael Ellerman

powerpc/64: Align bytes before fall back to .Lshort in powerpc64 memcmp()

Currently memcmp() 64bytes version in powerpc will fall back to .Lshort
(compare per byte mode) if either src or dst address is not 8 bytes aligned.
It can be opmitized in 2 situations:

1) if both addresses are with the same offset with 8 bytes boundary:
memcmp() can compare the unaligned bytes within 8 bytes boundary firstly
and then compare the rest 8-bytes-aligned content with .Llong mode.

2)  If src/dst addrs are not with the same offset of 8 bytes boundary:
memcmp() can align src addr with 8 bytes, increment dst addr accordingly,
 then load src with aligned mode and load dst with unaligned mode.

This patch optmizes memcmp() behavior in the above 2 situations.

Tested with both little/big endian. Performance result below is based on
little endian.

Following is the test result with src/dst having the same offset case:
(a similar result was observed when src/dst having different offset):
(1) 256 bytes
Test with the existing tools/testing/selftests/powerpc/stringloops/memcmp:
- without patch
	29.773018302 seconds time elapsed                                          ( +- 0.09% )
- with patch
	16.485568173 seconds time elapsed                                          ( +-  0.02% )
		-> There is ~+80% percent improvement

(2) 32 bytes
To observe performance impact on < 32 bytes, modify
tools/testing/selftests/powerpc/stringloops/memcmp.c with following:
-------
 #include <string.h>
 #include "utils.h"

-#define SIZE 256
+#define SIZE 32
 #define ITERATIONS 10000

 int test_memcmp(const void *s1, const void *s2, size_t n);
--------

- Without patch
	0.244746482 seconds time elapsed                                          ( +-  0.36%)
- with patch
	0.215069477 seconds time elapsed                                          ( +-  0.51%)
		-> There is ~+13% improvement

(3) 0~8 bytes
To observe <8 bytes performance impact, modify
tools/testing/selftests/powerpc/stringloops/memcmp.c with following:
-------
 #include <string.h>
 #include "utils.h"

-#define SIZE 256
-#define ITERATIONS 10000
+#define SIZE 8
+#define ITERATIONS 1000000

 int test_memcmp(const void *s1, const void *s2, size_t n);
-------
- Without patch
       1.845642503 seconds time elapsed                                          ( +- 0.12% )
- With patch
       1.849767135 seconds time elapsed                                          ( +- 0.26% )
		-> They are nearly the same. (-0.2%)
Signed-off-by: default avatarSimon Guo <wei.guo.simon@gmail.com>
Signed-off-by: default avatarMichael Ellerman <mpe@ellerman.id.au>
parent ca42d8d2
......@@ -24,28 +24,41 @@
#define rH r31
#ifdef __LITTLE_ENDIAN__
#define LH lhbrx
#define LW lwbrx
#define LD ldbrx
#else
#define LH lhzx
#define LW lwzx
#define LD ldx
#endif
/*
* There are 2 categories for memcmp:
* 1) src/dst has the same offset to the 8 bytes boundary. The handlers
* are named like .Lsameoffset_xxxx
* 2) src/dst has different offset to the 8 bytes boundary. The handlers
* are named like .Ldiffoffset_xxxx
*/
_GLOBAL(memcmp)
cmpdi cr1,r5,0
/* Use the short loop if both strings are not 8B aligned */
or r6,r3,r4
/* Use the short loop if the src/dst addresses are not
* with the same offset of 8 bytes align boundary.
*/
xor r6,r3,r4
andi. r6,r6,7
/* Use the short loop if length is less than 32B */
cmpdi cr6,r5,31
/* Fall back to short loop if compare at aligned addrs
* with less than 8 bytes.
*/
cmpdi cr6,r5,7
beq cr1,.Lzero
bne .Lshort
bgt cr6,.Llong
bgt cr6,.Lno_short
.Lshort:
mtctr r5
1: lbz rA,0(r3)
lbz rB,0(r4)
subf. rC,rB,rA
......@@ -78,11 +91,89 @@ _GLOBAL(memcmp)
li r3,0
blr
.Lno_short:
dcbt 0,r3
dcbt 0,r4
bne .Ldiffoffset_8bytes_make_align_start
.Lsameoffset_8bytes_make_align_start:
/* attempt to compare bytes not aligned with 8 bytes so that
* rest comparison can run based on 8 bytes alignment.
*/
andi. r6,r3,7
/* Try to compare the first double word which is not 8 bytes aligned:
* load the first double word at (src & ~7UL) and shift left appropriate
* bits before comparision.
*/
rlwinm r6,r3,3,26,28
beq .Lsameoffset_8bytes_aligned
clrrdi r3,r3,3
clrrdi r4,r4,3
LD rA,0,r3
LD rB,0,r4
sld rA,rA,r6
sld rB,rB,r6
cmpld cr0,rA,rB
srwi r6,r6,3
bne cr0,.LcmpAB_lightweight
subfic r6,r6,8
subf. r5,r6,r5
addi r3,r3,8
addi r4,r4,8
beq .Lzero
.Lsameoffset_8bytes_aligned:
/* now we are aligned with 8 bytes.
* Use .Llong loop if left cmp bytes are equal or greater than 32B.
*/
cmpdi cr6,r5,31
bgt cr6,.Llong
.Lcmp_lt32bytes:
/* compare 1 ~ 32 bytes, at least r3 addr is 8 bytes aligned now */
cmpdi cr5,r5,7
srdi r0,r5,3
ble cr5,.Lcmp_rest_lt8bytes
/* handle 8 ~ 31 bytes */
clrldi r5,r5,61
mtctr r0
2:
LD rA,0,r3
LD rB,0,r4
cmpld cr0,rA,rB
addi r3,r3,8
addi r4,r4,8
bne cr0,.LcmpAB_lightweight
bdnz 2b
cmpwi r5,0
beq .Lzero
.Lcmp_rest_lt8bytes:
/* Here we have only less than 8 bytes to compare with. at least s1
* Address is aligned with 8 bytes.
* The next double words are load and shift right with appropriate
* bits.
*/
subfic r6,r5,8
slwi r6,r6,3
LD rA,0,r3
LD rB,0,r4
srd rA,rA,r6
srd rB,rB,r6
cmpld cr0,rA,rB
bne cr0,.LcmpAB_lightweight
b .Lzero
.Lnon_zero:
mr r3,rC
blr
.Llong:
/* At least s1 addr is aligned with 8 bytes */
li off8,8
li off16,16
li off24,24
......@@ -232,4 +323,39 @@ _GLOBAL(memcmp)
ld r28,-32(r1)
ld r27,-40(r1)
blr
.LcmpAB_lightweight: /* skip NV GPRS restore */
li r3,1
bgtlr
li r3,-1
blr
.Ldiffoffset_8bytes_make_align_start:
/* now try to align s1 with 8 bytes */
rlwinm r6,r3,3,26,28
beq .Ldiffoffset_align_s1_8bytes
clrrdi r3,r3,3
LD rA,0,r3
LD rB,0,r4 /* unaligned load */
sld rA,rA,r6
srd rA,rA,r6
srd rB,rB,r6
cmpld cr0,rA,rB
srwi r6,r6,3
bne cr0,.LcmpAB_lightweight
subfic r6,r6,8
subf. r5,r6,r5
addi r3,r3,8
add r4,r4,r6
beq .Lzero
.Ldiffoffset_align_s1_8bytes:
/* now s1 is aligned with 8 bytes. */
cmpdi cr5,r5,31
ble cr5,.Lcmp_lt32bytes
b .Llong
EXPORT_SYMBOL(memcmp)
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