[PATCH v4 1/4] powerpc/64: Align bytes before fall back to .Lshort in powerpc64 memcmp()
From: <hidden>
Date: 2018-05-16 08:34:40
Subsystem:
linux for powerpc (32-bit and 64-bit), the rest · Maintainers:
Madhavan Srinivasan, Michael Ellerman, Linus Torvalds
From: Simon Guo <redacted>
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: Simon Guo <redacted>
---
arch/powerpc/lib/memcmp_64.S | 143 ++++++++++++++++++++++++++++++++++++++++---
1 file changed, 136 insertions(+), 7 deletions(-)
diff --git a/arch/powerpc/lib/memcmp_64.S b/arch/powerpc/lib/memcmp_64.S
index d75d18b..f20e883 100644
--- a/arch/powerpc/lib/memcmp_64.S
+++ b/arch/powerpc/lib/memcmp_64.S@@ -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 +91,90 @@ _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. + */ + clrlwi r6,r3,29 + rlwinm r6,r6,3,0,28 + 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 + subfc. 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 + rlwinm r6,r6,3,0,28 + 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 +324,41 @@ _GLOBAL(memcmp) ld r28,-32(r1) ld r27,-40(r1) blr + +.LcmpAB_lightweight: /* skip NV GPRS restore */ + li r3,1 + bgt cr0,8f + li r3,-1 +8: + blr + +.Ldiffoffset_8bytes_make_align_start: + /* now try to align s1 with 8 bytes */ + andi. r6,r3,0x7 + rlwinm r6,r6,3,0,28 + 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 + subfc. 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)
--
1.8.3.1