[PATCH] aarch64: Increase small and medium cases for __memcpy_generic

[PATCH] aarch64: Increase small and medium cases for __memcpy_generic

[Krzysztof Koch]

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Increase the upper bound on medium cases from 96 to 128 bytes.
Now, up to 128 bytes are copied unrolled.

Increase the upper bound on small cases from 16 to 32 bytes so that
copies of 17-32 bytes are not impacted by the larger medium case.

Benchmarking:
The attached figures show relative timing difference with respect
to 'memcpy_generic', which is the existing implementation.
'memcpy_med_128' denotes the the version of memcpy_generic with
only the medium case enlarged. The 'memcpy_med_128_small_32' numbers
are for the version of memcpy_generic submitted in this patch, which
has both medium and small cases enlarged. The figures were generated
using the script from:
https://www.sourceware.org/ml/libc-alpha/2019-10/msg00563.html

Depending on the platform, the performance improvement in the
bench-memcpy-random.c benchmark ranges from 6% to 20% between
the original and final version of memcpy.S

Tested against GLIBC testsuite and randomized tests.
---
 sysdeps/aarch64/memcpy.S | 82 +++++++++++++++++++++++++++---------------------
 1 file changed, 47 insertions(+), 35 deletions(-)

diff --git a/sysdeps/aarch64/memcpy.S b/sysdeps/aarch64/memcpy.S
index 6e4f4a7..10801aa 100644
--- a/sysdeps/aarch64/memcpy.S
+++ b/sysdeps/aarch64/memcpy.S
@@ -41,17 +41,19 @@
 #define C_h	x11
 #define D_l	x12
 #define D_h	x13
-#define E_l	src
-#define E_h	count
-#define F_l	srcend
-#define F_h	dst
+#define E_l	x14
+#define E_h	x15
+#define F_l	x16
+#define F_h	x17
 #define G_l	count
 #define G_h	dst
+#define H_l	src
+#define H_h	srcend
 #define tmp1	x14
 
-/* Copies are split into 3 main cases: small copies of up to 16 bytes,
-   medium copies of 17..96 bytes which are fully unrolled. Large copies
-   of more than 96 bytes align the destination and use an unrolled loop
+/* Copies are split into 3 main cases: small copies of up to 32 bytes,
+   medium copies of 33..128 bytes which are fully unrolled. Large copies
+   of more than 128 bytes align the destination and use an unrolled loop
    processing 64 bytes per iteration.
    In order to share code with memmove, small and medium copies read all
    data before writing, allowing any kind of overlap. So small, medium
@@ -73,7 +75,7 @@ ENTRY_ALIGN (MEMMOVE, 6)
 	DELOUSE (2)
 
 	sub	tmp1, dstin, src
-	cmp	count, 96
+	cmp	count, 128
 	ccmp	tmp1, count, 2, hi
 	b.lo	L(move_long)
 
@@ -89,31 +91,39 @@ ENTRY (MEMCPY)
 	prfm	PLDL1KEEP, [src]
 	add	srcend, src, count
 	add	dstend, dstin, count
-	cmp	count, 16
-	b.ls	L(copy16)
-	cmp	count, 96
+	cmp	count, 32
+	b.ls	L(copy32)
+	cmp	count, 128
 	b.hi	L(copy_long)
 
-	/* Medium copies: 17..96 bytes.  */
-	sub	tmp1, count, 1
+	/* Medium copies: 33..128 bytes.  */
 	ldp	A_l, A_h, [src]
-	tbnz	tmp1, 6, L(copy96)
-	ldp	D_l, D_h, [srcend, -16]
-	tbz	tmp1, 5, 1f
 	ldp	B_l, B_h, [src, 16]
 	ldp	C_l, C_h, [srcend, -32]
+	ldp	D_l, D_h, [srcend, -16]
+	cmp	count, 64
+	b.hi	L(copy128)
+	stp	A_l, A_h, [dstin]
 	stp	B_l, B_h, [dstin, 16]
 	stp	C_l, C_h, [dstend, -32]
-1:
-	stp	A_l, A_h, [dstin]
 	stp	D_l, D_h, [dstend, -16]
 	ret
 
 	.p2align 4
-	/* Small copies: 0..16 bytes.  */
-L(copy16):
-	cmp	count, 8
+	/* Small copies: 0..32 bytes.  */
+L(copy32):
+	/* 16-32 bytes.  */
+	cmp	count, 16
 	b.lo	1f
+	ldp	A_l, A_h, [src]
+	ldp	B_l, B_h, [srcend, -16]
+	stp	A_l, A_h, [dstin]
+	stp	B_l, B_h, [dstend, -16]
+	ret
+	.p2align 4
+1:
+	/* 8-15 bytes.  */
+	tbz	count, 3, 1f
 	ldr	A_l, [src]
 	ldr	A_h, [srcend, -8]
 	str	A_l, [dstin]
@@ -121,6 +131,7 @@ L(copy16):
 	ret
 	.p2align 4
 1:
+	/* 4-7 bytes.  */
 	tbz	count, 2, 1f
 	ldr	A_lw, [src]
 	ldr	A_hw, [srcend, -4]
@@ -142,24 +153,25 @@ L(copy16):
 2:	ret
 
 	.p2align 4
-	/* Copy 64..96 bytes.  Copy 64 bytes from the start and
-	   32 bytes from the end.  */
-L(copy96):
-	ldp	B_l, B_h, [src, 16]
-	ldp	C_l, C_h, [src, 32]
-	ldp	D_l, D_h, [src, 48]
-	ldp	E_l, E_h, [srcend, -32]
-	ldp	F_l, F_h, [srcend, -16]
+	/* Copy 65..128 bytes.  Copy 64 bytes from the start and
+	   64 bytes from the end.  */
+L(copy128):
+	ldp	E_l, E_h, [src, 32]
+	ldp	F_l, F_h, [src, 48]
+	ldp	G_l, G_h, [srcend, -64]
+	ldp	H_l, H_h, [srcend, -48]
 	stp	A_l, A_h, [dstin]
 	stp	B_l, B_h, [dstin, 16]
-	stp	C_l, C_h, [dstin, 32]
-	stp	D_l, D_h, [dstin, 48]
-	stp	E_l, E_h, [dstend, -32]
-	stp	F_l, F_h, [dstend, -16]
+	stp	E_l, E_h, [dstin, 32]
+	stp	F_l, F_h, [dstin, 48]
+	stp	G_l, G_h, [dstend, -64]
+	stp	H_l, H_h, [dstend, -48]
+	stp	C_l, C_h, [dstend, -32]
+	stp	D_l, D_h, [dstend, -16]
 	ret
 
 	/* Align DST to 16 byte alignment so that we don't cross cache line
-	   boundaries on both loads and stores.  There are at least 96 bytes
+	   boundaries on both loads and stores.  There are at least 128 bytes
 	   to copy, so copy 16 bytes unaligned and then align.  The loop
 	   copies 64 bytes per iteration and prefetches one iteration ahead.  */
 
@@ -215,7 +227,7 @@ L(move_long):
 	add	dstend, dstin, count
 
 	/* Align dstend to 16 byte alignment so that we don't cross cache line
-	   boundaries on both loads and stores.  There are at least 96 bytes
+	   boundaries on both loads and stores.  There are at least 128 bytes
 	   to copy, so copy 16 bytes unaligned and then align.  The loop
 	   copies 64 bytes per iteration and prefetches one iteration ahead.  */
 
-- 
1.9.1


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Re: [PATCH] aarch64: Increase small and medium cases for __memcpy_generic

[Szabolcs Nagy]

On 05/11/2019 17:35, Krzysztof Koch wrote:
> Increase the upper bound on medium cases from 96 to 128 bytes.
> Now, up to 128 bytes are copied unrolled.
> 
> Increase the upper bound on small cases from 16 to 32 bytes so that
> copies of 17-32 bytes are not impacted by the larger medium case.
> 
> Benchmarking:
> The attached figures show relative timing difference with respect
> to 'memcpy_generic', which is the existing implementation.
> 'memcpy_med_128' denotes the the version of memcpy_generic with
> only the medium case enlarged. The 'memcpy_med_128_small_32' numbers
> are for the version of memcpy_generic submitted in this patch, which
> has both medium and small cases enlarged. The figures were generated
> using the script from:
> https://www.sourceware.org/ml/libc-alpha/2019-10/msg00563.html
> 
> Depending on the platform, the performance improvement in the
> bench-memcpy-random.c benchmark ranges from 6% to 20% between
> the original and final version of memcpy.S
> 
> Tested against GLIBC testsuite and randomized tests.
> ---
>  sysdeps/aarch64/memcpy.S | 82 +++++++++++++++++++++++++++---------------------
>  1 file changed, 47 insertions(+), 35 deletions(-)

thanks, committed.