runtime: adjust the arm64 memmove and memclr to operate by word as much as they can

Not only is this an obvious optimization: benchmark old MB/s new MB/s speedup BenchmarkMemmove1-4 35.35 29.65 0.84x BenchmarkMemmove2-4 63.78 52.53 0.82x BenchmarkMemmove3-4 89.72 73.96 0.82x BenchmarkMemmove4-4 109.94 95.73 0.87x BenchmarkMemmove5-4 127.60 112.80 0.88x BenchmarkMemmove6-4 143.59 126.67 0.88x BenchmarkMemmove7-4 157.90 138.92 0.88x BenchmarkMemmove8-4 167.18 231.81 1.39x BenchmarkMemmove9-4 175.23 252.07 1.44x BenchmarkMemmove10-4 165.68 261.10 1.58x BenchmarkMemmove11-4 174.43 263.31 1.51x BenchmarkMemmove12-4 180.76 267.56 1.48x BenchmarkMemmove13-4 189.06 284.93 1.51x BenchmarkMemmove14-4 186.31 284.72 1.53x BenchmarkMemmove15-4 195.75 281.62 1.44x BenchmarkMemmove16-4 202.96 439.23 2.16x BenchmarkMemmove32-4 264.77 775.77 2.93x BenchmarkMemmove64-4 306.81 1209.64 3.94x BenchmarkMemmove128-4 357.03 1515.41 4.24x BenchmarkMemmove256-4 380.77 2066.01 5.43x BenchmarkMemmove512-4 385.05 2556.45 6.64x BenchmarkMemmove1024-4 381.23 2804.10 7.36x BenchmarkMemmove2048-4 379.06 2814.83 7.43x BenchmarkMemmove4096-4 387.43 3064.96 7.91x BenchmarkMemmoveUnaligned1-4 28.91 25.40 0.88x BenchmarkMemmoveUnaligned2-4 56.13 47.56 0.85x BenchmarkMemmoveUnaligned3-4 74.32 69.31 0.93x BenchmarkMemmoveUnaligned4-4 97.02 83.58 0.86x BenchmarkMemmoveUnaligned5-4 110.17 103.62 0.94x BenchmarkMemmoveUnaligned6-4 124.95 113.26 0.91x BenchmarkMemmoveUnaligned7-4 142.37 130.82 0.92x BenchmarkMemmoveUnaligned8-4 151.20 205.64 1.36x BenchmarkMemmoveUnaligned9-4 166.97 215.42 1.29x BenchmarkMemmoveUnaligned10-4 148.49 221.22 1.49x BenchmarkMemmoveUnaligned11-4 159.47 239.57 1.50x BenchmarkMemmoveUnaligned12-4 163.52 247.32 1.51x BenchmarkMemmoveUnaligned13-4 167.55 256.54 1.53x BenchmarkMemmoveUnaligned14-4 175.12 251.03 1.43x BenchmarkMemmoveUnaligned15-4 192.10 267.13 1.39x BenchmarkMemmoveUnaligned16-4 190.76 378.87 1.99x BenchmarkMemmoveUnaligned32-4 259.02 562.98 2.17x BenchmarkMemmoveUnaligned64-4 317.72 842.44 2.65x BenchmarkMemmoveUnaligned128-4 355.43 1274.49 3.59x BenchmarkMemmoveUnaligned256-4 378.17 1815.74 4.80x BenchmarkMemmoveUnaligned512-4 362.15 2180.81 6.02x BenchmarkMemmoveUnaligned1024-4 376.07 2453.58 6.52x BenchmarkMemmoveUnaligned2048-4 381.66 2568.32 6.73x BenchmarkMemmoveUnaligned4096-4 398.51 2669.36 6.70x BenchmarkMemclr5-4 113.83 107.93 0.95x BenchmarkMemclr16-4 223.84 389.63 1.74x BenchmarkMemclr64-4 421.99 1209.58 2.87x BenchmarkMemclr256-4 525.94 2411.58 4.59x BenchmarkMemclr4096-4 581.66 4372.20 7.52x BenchmarkMemclr65536-4 565.84 4747.48 8.39x BenchmarkGoMemclr5-4 194.63 160.31 0.82x BenchmarkGoMemclr16-4 295.30 630.07 2.13x BenchmarkGoMemclr64-4 480.24 1884.03 3.92x BenchmarkGoMemclr256-4 540.23 2926.49 5.42x but it turns out that it's necessary to avoid the GC seeing partially written pointers. It's of course possible to be more sophisticated (using ldp/stp to move 16 bytes at a time in the core loop and unrolling the tail copying loops being the obvious ideas) but I wanted something simple and (reasonably) obviously correct. Fixes #12552 Change-Id: Iaeaf8a812cd06f4747ba2f792de1ded738890735 Reviewed-on: https://go-review.googlesource.com/14813 Reviewed-by: Austin Clements <austin@google.com>
2024-11-18 11:44:45 -07:00 · 2015-09-22 14:34:39 +12:00 · 2015-09-22 14:34:39 +12:00 · 168a51b3a1
commit 168a51b3a1
parent 46b97e7579
3 changed files with 127 additions and 18 deletions
--- a/src/runtime/memclr_arm64.s
+++ b/src/runtime/memclr_arm64.s
@ -8,11 +8,30 @@
 TEXT runtime·memclr(SB),NOSPLIT,$0-16
 	MOVD	ptr+0(FP), R3
 	MOVD	n+8(FP), R4
-	CMP	$0, R4
+	// TODO(mwhudson): this is written this way to avoid tickling
+	// warnings from addpool when written as AND $7, R4, R6 (see
+	// https://golang.org/issue/12708)
+	AND	$~7, R4, R5	// R5 is N&~7
+	SUB	R5, R4, R6	// R6 is N&7
+
+	CMP	$0, R5
+	BEQ	nowords
+
+	ADD	R3, R5, R5
+
+wordloop: // TODO: Optimize for unaligned ptr.
+	MOVD.P	$0, 8(R3)
+	CMP	R3, R5
+	BNE	wordloop
+nowords:
+        CMP	$0, R6
        BEQ	done
-	ADD	R3, R4, R4
+
+	ADD	R3, R6, R6
+
+byteloop:
 	MOVBU.P	$0, 1(R3)
-	CMP	R3, R4
-	BNE	-2(PC)
+	CMP	R3, R6
+	BNE	byteloop
 done:
 	RET
--- a/src/runtime/memmove_arm64.s
+++ b/src/runtime/memmove_arm64.s
@ -14,23 +14,78 @@ TEXT runtime·memmove(SB), NOSPLIT, $-8-24
 	RET

 check:
+	AND	$~7, R5, R7	// R7 is N&~7
+	// TODO(mwhudson): this is written this way to avoid tickling
+	// warnings from addpool when written as AND $7, R5, R6 (see
+	// https://golang.org/issue/12708)
+	SUB	R7, R5, R6	// R6 is N&7
+
 	CMP	R3, R4
 	BLT	backward

-	ADD	R3, R5
-loop:
-	MOVBU.P	1(R4), R6
-	MOVBU.P	R6, 1(R3)
-	CMP	R3, R5
-	BNE	loop
+	// Copying forward proceeds by copying R7/8 words then copying R6 bytes.
+	// R3 and R4 are advanced as we copy.
+
+        // (There may be implementations of armv8 where copying by bytes until
+        // at least one of source or dest is word aligned is a worthwhile
+        // optimization, but the on the one tested so far (xgene) it did not
+        // make a significance difference.)
+
+	CMP	$0, R7		// Do we need to do any word-by-word copying?
+	BEQ	noforwardlarge
+
+	ADD	R3, R7, R9	// R9 points just past where we copy by word
+
+forwardlargeloop:
+	MOVD.P	8(R4), R8	// R8 is just a scratch register
+	MOVD.P	R8, 8(R3)
+	CMP	R3, R9
+	BNE	forwardlargeloop
+
+noforwardlarge:
+	CMP	$0, R6		// Do we need to do any byte-by-byte copying?
+	BNE	forwardtail
+	RET
+
+forwardtail:
+	ADD	R3, R6, R9	// R9 points just past the destination memory
+
+forwardtailloop:
+	MOVBU.P 1(R4), R8
+	MOVBU.P	R8, 1(R3)
+	CMP	R3, R9
+	BNE	forwardtailloop
 	RET

 backward:
-	ADD	R5, R4
-	ADD	R3, R5
-loop1:
-	MOVBU.W	-1(R4), R6
-	MOVBU.W	R6, -1(R5)
-	CMP	R3, R5
-	BNE	loop1
+	// Copying backwards proceeds by copying R6 bytes then copying R7/8 words.
+	// R3 and R4 are advanced to the end of the destination/source buffers
+	// respectively and moved back as we copy.
+
+	ADD	R4, R5, R4	// R4 points just past the last source byte
+	ADD	R3, R5, R3	// R3 points just past the last destination byte
+
+	CMP	$0, R6		// Do we need to do any byte-by-byte copying?
+	BEQ	nobackwardtail
+
+	SUB	R6, R3, R9	// R9 points at the lowest destination byte that should be copied by byte.
+backwardtailloop:
+	MOVBU.W	-1(R4), R8
+	MOVBU.W	R8, -1(R3)
+	CMP	R9, R3
+	BNE	backwardtailloop
+
+nobackwardtail:
+	CMP     $0, R7		// Do we need to do any word-by-word copying?
+	BNE	backwardlarge
+	RET
+
+backwardlarge:
+        SUB	R7, R3, R9      // R9 points at the lowest destination byte
+
+backwardlargeloop:
+	MOVD.W	-8(R4), R8
+	MOVD.W	R8, -8(R3)
+	CMP	R9, R3
+	BNE	backwardlargeloop
 	RET
--- a/src/runtime/memmove_test.go
+++ b/src/runtime/memmove_test.go
@ -116,6 +116,41 @@ func BenchmarkMemmove1024(b *testing.B) { bmMemmove(b, 1024) }
 func BenchmarkMemmove2048(b *testing.B) { bmMemmove(b, 2048) }
 func BenchmarkMemmove4096(b *testing.B) { bmMemmove(b, 4096) }

+func bmMemmoveUnaligned(b *testing.B, n int) {
+	x := make([]byte, n+1)
+	y := make([]byte, n)
+	b.SetBytes(int64(n))
+	for i := 0; i < b.N; i++ {
+		copy(x[1:], y)
+	}
+}
+
+func BenchmarkMemmoveUnaligned0(b *testing.B)    { bmMemmoveUnaligned(b, 0) }
+func BenchmarkMemmoveUnaligned1(b *testing.B)    { bmMemmoveUnaligned(b, 1) }
+func BenchmarkMemmoveUnaligned2(b *testing.B)    { bmMemmoveUnaligned(b, 2) }
+func BenchmarkMemmoveUnaligned3(b *testing.B)    { bmMemmoveUnaligned(b, 3) }
+func BenchmarkMemmoveUnaligned4(b *testing.B)    { bmMemmoveUnaligned(b, 4) }
+func BenchmarkMemmoveUnaligned5(b *testing.B)    { bmMemmoveUnaligned(b, 5) }
+func BenchmarkMemmoveUnaligned6(b *testing.B)    { bmMemmoveUnaligned(b, 6) }
+func BenchmarkMemmoveUnaligned7(b *testing.B)    { bmMemmoveUnaligned(b, 7) }
+func BenchmarkMemmoveUnaligned8(b *testing.B)    { bmMemmoveUnaligned(b, 8) }
+func BenchmarkMemmoveUnaligned9(b *testing.B)    { bmMemmoveUnaligned(b, 9) }
+func BenchmarkMemmoveUnaligned10(b *testing.B)   { bmMemmoveUnaligned(b, 10) }
+func BenchmarkMemmoveUnaligned11(b *testing.B)   { bmMemmoveUnaligned(b, 11) }
+func BenchmarkMemmoveUnaligned12(b *testing.B)   { bmMemmoveUnaligned(b, 12) }
+func BenchmarkMemmoveUnaligned13(b *testing.B)   { bmMemmoveUnaligned(b, 13) }
+func BenchmarkMemmoveUnaligned14(b *testing.B)   { bmMemmoveUnaligned(b, 14) }
+func BenchmarkMemmoveUnaligned15(b *testing.B)   { bmMemmoveUnaligned(b, 15) }
+func BenchmarkMemmoveUnaligned16(b *testing.B)   { bmMemmoveUnaligned(b, 16) }
+func BenchmarkMemmoveUnaligned32(b *testing.B)   { bmMemmoveUnaligned(b, 32) }
+func BenchmarkMemmoveUnaligned64(b *testing.B)   { bmMemmoveUnaligned(b, 64) }
+func BenchmarkMemmoveUnaligned128(b *testing.B)  { bmMemmoveUnaligned(b, 128) }
+func BenchmarkMemmoveUnaligned256(b *testing.B)  { bmMemmoveUnaligned(b, 256) }
+func BenchmarkMemmoveUnaligned512(b *testing.B)  { bmMemmoveUnaligned(b, 512) }
+func BenchmarkMemmoveUnaligned1024(b *testing.B) { bmMemmoveUnaligned(b, 1024) }
+func BenchmarkMemmoveUnaligned2048(b *testing.B) { bmMemmoveUnaligned(b, 2048) }
+func BenchmarkMemmoveUnaligned4096(b *testing.B) { bmMemmoveUnaligned(b, 4096) }
+
 func TestMemclr(t *testing.T) {
 	size := 512
 	if testing.Short() {