[PATCH v2 1/3] riscv: optimized memcpy

From: Matteo Croce
Date: Wed Jun 16 2021 - 21:26:10 EST

From: Matteo Croce <mcroce@xxxxxxxxxxxxx>

Write a C version of memcpy() which uses the biggest data size allowed,
without generating unaligned accesses.

The procedure is made of three steps:
First copy data one byte at time until the destination buffer is aligned
to a long boundary.
Then copy the data one long at time shifting the current and the next u8
to compose a long at every cycle.
Finally, copy the remainder one byte at time.

On a BeagleV, the TCP RX throughput increased by 45%:

before:

$ iperf3 -c beaglev
Connecting to host beaglev, port 5201
[ 5] local 192.168.85.6 port 44840 connected to 192.168.85.48 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 76.4 MBytes 641 Mbits/sec 27 624 KBytes
[ 5] 1.00-2.00 sec 72.5 MBytes 608 Mbits/sec 0 708 KBytes
[ 5] 2.00-3.00 sec 73.8 MBytes 619 Mbits/sec 10 451 KBytes
[ 5] 3.00-4.00 sec 72.5 MBytes 608 Mbits/sec 0 564 KBytes
[ 5] 4.00-5.00 sec 73.8 MBytes 619 Mbits/sec 0 658 KBytes
[ 5] 5.00-6.00 sec 73.8 MBytes 619 Mbits/sec 14 522 KBytes
[ 5] 6.00-7.00 sec 73.8 MBytes 619 Mbits/sec 0 621 KBytes
[ 5] 7.00-8.00 sec 72.5 MBytes 608 Mbits/sec 0 706 KBytes
[ 5] 8.00-9.00 sec 73.8 MBytes 619 Mbits/sec 20 580 KBytes
[ 5] 9.00-10.00 sec 73.8 MBytes 619 Mbits/sec 0 672 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 736 MBytes 618 Mbits/sec 71 sender
[ 5] 0.00-10.01 sec 733 MBytes 615 Mbits/sec receiver

after:

$ iperf3 -c beaglev
Connecting to host beaglev, port 5201
[ 5] local 192.168.85.6 port 44864 connected to 192.168.85.48 port 5201
[ ID] Interval Transfer Bitrate Retr Cwnd
[ 5] 0.00-1.00 sec 109 MBytes 912 Mbits/sec 48 559 KBytes
[ 5] 1.00-2.00 sec 108 MBytes 902 Mbits/sec 0 690 KBytes
[ 5] 2.00-3.00 sec 106 MBytes 891 Mbits/sec 36 396 KBytes
[ 5] 3.00-4.00 sec 108 MBytes 902 Mbits/sec 0 567 KBytes
[ 5] 4.00-5.00 sec 106 MBytes 891 Mbits/sec 0 699 KBytes
[ 5] 5.00-6.00 sec 106 MBytes 891 Mbits/sec 32 414 KBytes
[ 5] 6.00-7.00 sec 106 MBytes 891 Mbits/sec 0 583 KBytes
[ 5] 7.00-8.00 sec 106 MBytes 891 Mbits/sec 0 708 KBytes
[ 5] 8.00-9.00 sec 106 MBytes 891 Mbits/sec 28 433 KBytes
[ 5] 9.00-10.00 sec 108 MBytes 902 Mbits/sec 0 591 KBytes
- - - - - - - - - - - - - - - - - - - - - - - - -
[ ID] Interval Transfer Bitrate Retr
[ 5] 0.00-10.00 sec 1.04 GBytes 897 Mbits/sec 144 sender
[ 5] 0.00-10.01 sec 1.04 GBytes 894 Mbits/sec receiver

And the decreased CPU time of the memcpy() is observable with perf top.
This is the `perf top -Ue task-clock` output when doing the test:

before:

Overhead Shared O Symbol
42.22% [kernel] [k] memcpy
35.00% [kernel] [k] __asm_copy_to_user
3.50% [kernel] [k] sifive_l2_flush64_range
2.30% [kernel] [k] stmmac_napi_poll_rx
1.11% [kernel] [k] memset

after:

Overhead Shared O Symbol
45.69% [kernel] [k] __asm_copy_to_user
29.06% [kernel] [k] memcpy
4.09% [kernel] [k] sifive_l2_flush64_range
2.77% [kernel] [k] stmmac_napi_poll_rx
1.24% [kernel] [k] memset

Signed-off-by: Matteo Croce <mcroce@xxxxxxxxxxxxx>
---
arch/riscv/include/asm/string.h | 8 ++-
arch/riscv/kernel/riscv_ksyms.c | 2 -
arch/riscv/lib/Makefile | 2 +-
arch/riscv/lib/memcpy.S | 108 --------------------------------
arch/riscv/lib/string.c | 94 +++++++++++++++++++++++++++
5 files changed, 101 insertions(+), 113 deletions(-)
delete mode 100644 arch/riscv/lib/memcpy.S
create mode 100644 arch/riscv/lib/string.c

diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 909049366555..6b5d6fc3eab4 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -12,9 +12,13 @@
#define __HAVE_ARCH_MEMSET
extern asmlinkage void *memset(void *, int, size_t);
extern asmlinkage void *__memset(void *, int, size_t);
+
+#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE
#define __HAVE_ARCH_MEMCPY
-extern asmlinkage void *memcpy(void *, const void *, size_t);
-extern asmlinkage void *__memcpy(void *, const void *, size_t);
+extern void *memcpy(void *dest, const void *src, size_t count);
+extern void *__memcpy(void *dest, const void *src, size_t count);
+#endif
+
#define __HAVE_ARCH_MEMMOVE
extern asmlinkage void *memmove(void *, const void *, size_t);
extern asmlinkage void *__memmove(void *, const void *, size_t);
diff --git a/arch/riscv/kernel/riscv_ksyms.c b/arch/riscv/kernel/riscv_ksyms.c
index 5ab1c7e1a6ed..3f6d512a5b97 100644
--- a/arch/riscv/kernel/riscv_ksyms.c
+++ b/arch/riscv/kernel/riscv_ksyms.c
@@ -10,8 +10,6 @@
* Assembly functions that may be used (directly or indirectly) by modules
*/
EXPORT_SYMBOL(memset);
-EXPORT_SYMBOL(memcpy);
EXPORT_SYMBOL(memmove);
EXPORT_SYMBOL(__memset);
-EXPORT_SYMBOL(__memcpy);
EXPORT_SYMBOL(__memmove);
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 25d5c9664e57..2ffe85d4baee 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -1,9 +1,9 @@
# SPDX-License-Identifier: GPL-2.0-only
lib-y += delay.o
-lib-y += memcpy.o
lib-y += memset.o
lib-y += memmove.o
lib-$(CONFIG_MMU) += uaccess.o
lib-$(CONFIG_64BIT) += tishift.o
+lib-$(CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE) += string.o

obj-$(CONFIG_FUNCTION_ERROR_INJECTION) += error-inject.o
diff --git a/arch/riscv/lib/memcpy.S b/arch/riscv/lib/memcpy.S
deleted file mode 100644
index 51ab716253fa..000000000000
--- a/arch/riscv/lib/memcpy.S
+++ /dev/null
@@ -1,108 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0-only */
-/*
- * Copyright (C) 2013 Regents of the University of California
- */
-
-#include <linux/linkage.h>
-#include <asm/asm.h>
-
-/* void *memcpy(void *, const void *, size_t) */
-ENTRY(__memcpy)
-WEAK(memcpy)
- move t6, a0 /* Preserve return value */
-
- /* Defer to byte-oriented copy for small sizes */
- sltiu a3, a2, 128
- bnez a3, 4f
- /* Use word-oriented copy only if low-order bits match */
- andi a3, t6, SZREG-1
- andi a4, a1, SZREG-1
- bne a3, a4, 4f
-
- beqz a3, 2f /* Skip if already aligned */
- /*
- * Round to nearest double word-aligned address
- * greater than or equal to start address
- */
- andi a3, a1, ~(SZREG-1)
- addi a3, a3, SZREG
- /* Handle initial misalignment */
- sub a4, a3, a1
-1:
- lb a5, 0(a1)
- addi a1, a1, 1
- sb a5, 0(t6)
- addi t6, t6, 1
- bltu a1, a3, 1b
- sub a2, a2, a4 /* Update count */
-
-2:
- andi a4, a2, ~((16*SZREG)-1)
- beqz a4, 4f
- add a3, a1, a4
-3:
- REG_L a4, 0(a1)
- REG_L a5, SZREG(a1)
- REG_L a6, 2*SZREG(a1)
- REG_L a7, 3*SZREG(a1)
- REG_L t0, 4*SZREG(a1)
- REG_L t1, 5*SZREG(a1)
- REG_L t2, 6*SZREG(a1)
- REG_L t3, 7*SZREG(a1)
- REG_L t4, 8*SZREG(a1)
- REG_L t5, 9*SZREG(a1)
- REG_S a4, 0(t6)
- REG_S a5, SZREG(t6)
- REG_S a6, 2*SZREG(t6)
- REG_S a7, 3*SZREG(t6)
- REG_S t0, 4*SZREG(t6)
- REG_S t1, 5*SZREG(t6)
- REG_S t2, 6*SZREG(t6)
- REG_S t3, 7*SZREG(t6)
- REG_S t4, 8*SZREG(t6)
- REG_S t5, 9*SZREG(t6)
- REG_L a4, 10*SZREG(a1)
- REG_L a5, 11*SZREG(a1)
- REG_L a6, 12*SZREG(a1)
- REG_L a7, 13*SZREG(a1)
- REG_L t0, 14*SZREG(a1)
- REG_L t1, 15*SZREG(a1)
- addi a1, a1, 16*SZREG
- REG_S a4, 10*SZREG(t6)
- REG_S a5, 11*SZREG(t6)
- REG_S a6, 12*SZREG(t6)
- REG_S a7, 13*SZREG(t6)
- REG_S t0, 14*SZREG(t6)
- REG_S t1, 15*SZREG(t6)
- addi t6, t6, 16*SZREG
- bltu a1, a3, 3b
- andi a2, a2, (16*SZREG)-1 /* Update count */
-
-4:
- /* Handle trailing misalignment */
- beqz a2, 6f
- add a3, a1, a2
-
- /* Use word-oriented copy if co-aligned to word boundary */
- or a5, a1, t6
- or a5, a5, a3
- andi a5, a5, 3
- bnez a5, 5f
-7:
- lw a4, 0(a1)
- addi a1, a1, 4
- sw a4, 0(t6)
- addi t6, t6, 4
- bltu a1, a3, 7b
-
- ret
-
-5:
- lb a4, 0(a1)
- addi a1, a1, 1
- sb a4, 0(t6)
- addi t6, t6, 1
- bltu a1, a3, 5b
-6:
- ret
-END(__memcpy)
diff --git a/arch/riscv/lib/string.c b/arch/riscv/lib/string.c
new file mode 100644
index 000000000000..694352d21c21
--- /dev/null
+++ b/arch/riscv/lib/string.c
@@ -0,0 +1,94 @@
+// SPDX-License-Identifier: GPL-2.0-only
+/*
+ * String functions optimized for hardware which doesn't
+ * handle unaligned memory accesses efficiently.
+ *
+ * Copyright (C) 2021 Matteo Croce
+ */
+
+#include <linux/types.h>
+#include <linux/module.h>
+
+/* Minimum size for a word copy to be convenient */
+#define MIN_THRESHOLD (BITS_PER_LONG / 8 * 2)
+
+/* convenience union to avoid cast between different pointer types */
+union types {
+ u8 *u8;
+ unsigned long *ulong;
+ uintptr_t uptr;
+};
+
+union const_types {
+ const u8 *u8;
+ unsigned long *ulong;
+};
+
+void __weak *memcpy(void *dest, const void *src, size_t count)
+{
+ const int bytes_long = BITS_PER_LONG / 8;
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+ const int mask = bytes_long - 1;
+ const int distance = (src - dest) & mask;
+#endif
+ union const_types s = { .u8 = src };
+ union types d = { .u8 = dest };
+
+#ifndef CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS
+ if (count < MIN_THRESHOLD)
+ goto copy_remainder;
+
+ /* copy a byte at time until destination is aligned */
+ for (; count && d.uptr & mask; count--)
+ *d.u8++ = *s.u8++;
+
+ if (distance) {
+ unsigned long last, next;
+
+ /* move s backward to the previous alignment boundary */
+ s.u8 -= distance;
+
+ /* 32/64 bit wide copy from s to d.
+ * d is aligned now but s is not, so read s alignment wise,
+ * and do proper shift to get the right value.
+ * Works only on Little Endian machines.
+ */
+ for (next = s.ulong[0]; count >= bytes_long + mask; count -= bytes_long) {
+ last = next;
+ next = s.ulong[1];
+
+ d.ulong[0] = last >> (distance * 8) |
+ next << ((bytes_long - distance) * 8);
+
+ d.ulong++;
+ s.ulong++;
+ }
+
+ /* restore s with the original offset */
+ s.u8 += distance;
+ } else
+#endif
+ {
+ /* if the source and dest lower bits are the same, do a simple
+ * 32/64 bit wide copy.
+ */
+ for (; count >= bytes_long; count -= bytes_long)
+ *d.ulong++ = *s.ulong++;
+ }
+
+ /* suppress warning when CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS=y */
+ goto copy_remainder;
+
+copy_remainder:
+ while (count--)
+ *d.u8++ = *s.u8++;
+
+ return dest;
+}
+EXPORT_SYMBOL(memcpy);
+
+void *__memcpy(void *dest, const void *src, size_t count)
+{
+ return memcpy(dest, src, count);
+}
+EXPORT_SYMBOL(__memcpy);
--
2.31.1