From: Matteo Croce <[email protected]>
Replace the assembly mem{cpy,move,set} with C equivalent.
Try to access RAM with the largest bit width possible, but without
doing unaligned accesses.
A further improvement could be to use multiple read and writes as the
assembly version was trying to do.
Tested on a BeagleV Starlight with a SiFive U74 core, where the
improvement is noticeable.
v4 -> v5:
- call __memcpy() instead of memcpy() in memmove()
v3 -> v4:
- incorporate changes from proposed generic version:
https://lore.kernel.org/lkml/[email protected]/
v2 -> v3:
- alias mem* to __mem* and not viceversa
- use __alias instead of a tail call
v1 -> v2:
- reduce the threshold from 64 to 16 bytes
- fix KASAN build
- optimize memset
Matteo Croce (3):
riscv: optimized memcpy
riscv: optimized memmove
riscv: optimized memset
arch/riscv/include/asm/string.h | 18 ++--
arch/riscv/kernel/Makefile | 1 -
arch/riscv/kernel/riscv_ksyms.c | 17 ----
arch/riscv/lib/Makefile | 4 +-
arch/riscv/lib/memcpy.S | 108 ----------------------
arch/riscv/lib/memmove.S | 64 -------------
arch/riscv/lib/memset.S | 113 -----------------------
arch/riscv/lib/string.c | 154 ++++++++++++++++++++++++++++++++
8 files changed, 164 insertions(+), 315 deletions(-)
delete mode 100644 arch/riscv/kernel/riscv_ksyms.c
delete mode 100644 arch/riscv/lib/memcpy.S
delete mode 100644 arch/riscv/lib/memmove.S
delete mode 100644 arch/riscv/lib/memset.S
create mode 100644 arch/riscv/lib/string.c
--
2.31.1
From: Matteo Croce <[email protected]>
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 <[email protected]>
Reported-by: kernel test robot <[email protected]>
---
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 | 90 ++++++++++++++++++++++++++
5 files changed, 97 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..bfc912ee23f8
--- /dev/null
+++ b/arch/riscv/lib/string.c
@@ -0,0 +1,90 @@
+// 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 BYTES_LONG sizeof(long)
+#define WORD_MASK (BYTES_LONG - 1)
+#define MIN_THRESHOLD (BYTES_LONG * 2)
+
+/* convenience union to avoid cast between different pointer types */
+union types {
+ u8 *as_u8;
+ unsigned long *as_ulong;
+ uintptr_t as_uptr;
+};
+
+union const_types {
+ const u8 *as_u8;
+ unsigned long *as_ulong;
+ uintptr_t as_uptr;
+};
+
+void *__memcpy(void *dest, const void *src, size_t count)
+{
+ union const_types s = { .as_u8 = src };
+ union types d = { .as_u8 = dest };
+ int distance = 0;
+
+ if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
+ if (count < MIN_THRESHOLD)
+ goto copy_remainder;
+
+ /* Copy a byte at time until destination is aligned. */
+ for (; d.as_uptr & WORD_MASK; count--)
+ *d.as_u8++ = *s.as_u8++;
+
+ distance = s.as_uptr & WORD_MASK;
+ }
+
+ if (distance) {
+ unsigned long last, next;
+
+ /*
+ * s is distance bytes ahead of d, and d just reached
+ * the alignment boundary. Move s backward to word align it
+ * and shift data to compensate for distance, in order to do
+ * word-by-word copy.
+ */
+ s.as_u8 -= distance;
+
+ next = s.as_ulong[0];
+ for (; count >= BYTES_LONG; count -= BYTES_LONG) {
+ last = next;
+ next = s.as_ulong[1];
+
+ d.as_ulong[0] = last >> (distance * 8) |
+ next << ((BYTES_LONG - distance) * 8);
+
+ d.as_ulong++;
+ s.as_ulong++;
+ }
+
+ /* Restore s with the original offset. */
+ s.as_u8 += distance;
+ } else {
+ /*
+ * 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.as_ulong++ = *s.as_ulong++;
+ }
+
+copy_remainder:
+ while (count--)
+ *d.as_u8++ = *s.as_u8++;
+
+ return dest;
+}
+EXPORT_SYMBOL(__memcpy);
+
+void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);
+EXPORT_SYMBOL(memcpy);
--
2.31.1
From: Matteo Croce <[email protected]>
When the destination buffer is before the source one, or when the
buffers doesn't overlap, it's safe to use memcpy() instead, which is
optimized to use a bigger data size possible.
Signed-off-by: Matteo Croce <[email protected]>
Reported-by: kernel test robot <[email protected]>
---
arch/riscv/include/asm/string.h | 6 ++--
arch/riscv/kernel/riscv_ksyms.c | 2 --
arch/riscv/lib/Makefile | 1 -
arch/riscv/lib/memmove.S | 64 ---------------------------------
arch/riscv/lib/string.c | 23 ++++++++++++
5 files changed, 26 insertions(+), 70 deletions(-)
delete mode 100644 arch/riscv/lib/memmove.S
diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
index 6b5d6fc3eab4..25d9b9078569 100644
--- a/arch/riscv/include/asm/string.h
+++ b/arch/riscv/include/asm/string.h
@@ -17,11 +17,11 @@ extern asmlinkage void *__memset(void *, int, size_t);
#define __HAVE_ARCH_MEMCPY
extern void *memcpy(void *dest, const void *src, size_t count);
extern void *__memcpy(void *dest, const void *src, size_t count);
+#define __HAVE_ARCH_MEMMOVE
+extern void *memmove(void *dest, const void *src, size_t count);
+extern void *__memmove(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);
/* For those files which don't want to check by kasan. */
#if defined(CONFIG_KASAN) && !defined(__SANITIZE_ADDRESS__)
#define memcpy(dst, src, len) __memcpy(dst, src, len)
diff --git a/arch/riscv/kernel/riscv_ksyms.c b/arch/riscv/kernel/riscv_ksyms.c
index 3f6d512a5b97..361565c4db7e 100644
--- a/arch/riscv/kernel/riscv_ksyms.c
+++ b/arch/riscv/kernel/riscv_ksyms.c
@@ -10,6 +10,4 @@
* Assembly functions that may be used (directly or indirectly) by modules
*/
EXPORT_SYMBOL(memset);
-EXPORT_SYMBOL(memmove);
EXPORT_SYMBOL(__memset);
-EXPORT_SYMBOL(__memmove);
diff --git a/arch/riscv/lib/Makefile b/arch/riscv/lib/Makefile
index 2ffe85d4baee..484f5ff7b508 100644
--- a/arch/riscv/lib/Makefile
+++ b/arch/riscv/lib/Makefile
@@ -1,7 +1,6 @@
# SPDX-License-Identifier: GPL-2.0-only
lib-y += delay.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
diff --git a/arch/riscv/lib/memmove.S b/arch/riscv/lib/memmove.S
deleted file mode 100644
index 07d1d2152ba5..000000000000
--- a/arch/riscv/lib/memmove.S
+++ /dev/null
@@ -1,64 +0,0 @@
-/* SPDX-License-Identifier: GPL-2.0 */
-
-#include <linux/linkage.h>
-#include <asm/asm.h>
-
-ENTRY(__memmove)
-WEAK(memmove)
- move t0, a0
- move t1, a1
-
- beq a0, a1, exit_memcpy
- beqz a2, exit_memcpy
- srli t2, a2, 0x2
-
- slt t3, a0, a1
- beqz t3, do_reverse
-
- andi a2, a2, 0x3
- li t4, 1
- beqz t2, byte_copy
-
-word_copy:
- lw t3, 0(a1)
- addi t2, t2, -1
- addi a1, a1, 4
- sw t3, 0(a0)
- addi a0, a0, 4
- bnez t2, word_copy
- beqz a2, exit_memcpy
- j byte_copy
-
-do_reverse:
- add a0, a0, a2
- add a1, a1, a2
- andi a2, a2, 0x3
- li t4, -1
- beqz t2, reverse_byte_copy
-
-reverse_word_copy:
- addi a1, a1, -4
- addi t2, t2, -1
- lw t3, 0(a1)
- addi a0, a0, -4
- sw t3, 0(a0)
- bnez t2, reverse_word_copy
- beqz a2, exit_memcpy
-
-reverse_byte_copy:
- addi a0, a0, -1
- addi a1, a1, -1
-
-byte_copy:
- lb t3, 0(a1)
- addi a2, a2, -1
- sb t3, 0(a0)
- add a1, a1, t4
- add a0, a0, t4
- bnez a2, byte_copy
-
-exit_memcpy:
- move a0, t0
- move a1, t1
- ret
-END(__memmove)
diff --git a/arch/riscv/lib/string.c b/arch/riscv/lib/string.c
index bfc912ee23f8..4442ca5ef13c 100644
--- a/arch/riscv/lib/string.c
+++ b/arch/riscv/lib/string.c
@@ -88,3 +88,26 @@ EXPORT_SYMBOL(__memcpy);
void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);
EXPORT_SYMBOL(memcpy);
+
+/*
+ * Simply check if the buffer overlaps an call memcpy() in case,
+ * otherwise do a simple one byte at time backward copy.
+ */
+void *__memmove(void *dest, const void *src, size_t count)
+{
+ if (dest < src || src + count <= dest)
+ return __memcpy(dest, src, count);
+
+ if (dest > src) {
+ const char *s = src + count;
+ char *tmp = dest + count;
+
+ while (count--)
+ *--tmp = *--s;
+ }
+ return dest;
+}
+EXPORT_SYMBOL(__memmove);
+
+void *memmove(void *dest, const void *src, size_t count) __weak __alias(__memmove);
+EXPORT_SYMBOL(memmove);
--
2.31.1
On Thu, Sep 30, 2021 at 1:22 AM Matteo Croce <[email protected]> wrote:
>
> From: Matteo Croce <[email protected]>
>
> 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 <[email protected]>
> Reported-by: kernel test robot <[email protected]>
> ---
> 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 | 90 ++++++++++++++++++++++++++
> 5 files changed, 97 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
What's the problem with the -O3 & -Os? If the user uses
CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 that will cause bad performance
for memcpy?
Seems asm version is more compatible?
> #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..bfc912ee23f8
> --- /dev/null
> +++ b/arch/riscv/lib/string.c
> @@ -0,0 +1,90 @@
> +// 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 BYTES_LONG sizeof(long)
> +#define WORD_MASK (BYTES_LONG - 1)
> +#define MIN_THRESHOLD (BYTES_LONG * 2)
> +
> +/* convenience union to avoid cast between different pointer types */
> +union types {
> + u8 *as_u8;
> + unsigned long *as_ulong;
> + uintptr_t as_uptr;
> +};
> +
> +union const_types {
> + const u8 *as_u8;
> + unsigned long *as_ulong;
> + uintptr_t as_uptr;
> +};
> +
> +void *__memcpy(void *dest, const void *src, size_t count)
How about using __attribute__((optimize("-O2"))) here to replace your
previous "#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE"?
> +{
> + union const_types s = { .as_u8 = src };
> + union types d = { .as_u8 = dest };
> + int distance = 0;
> +
> + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
> + if (count < MIN_THRESHOLD)
> + goto copy_remainder;
> +
> + /* Copy a byte at time until destination is aligned. */
> + for (; d.as_uptr & WORD_MASK; count--)
> + *d.as_u8++ = *s.as_u8++;
> +
> + distance = s.as_uptr & WORD_MASK;
> + }
> +
> + if (distance) {
> + unsigned long last, next;
> +
> + /*
> + * s is distance bytes ahead of d, and d just reached
> + * the alignment boundary. Move s backward to word align it
> + * and shift data to compensate for distance, in order to do
> + * word-by-word copy.
> + */
> + s.as_u8 -= distance;
> +
> + next = s.as_ulong[0];
> + for (; count >= BYTES_LONG; count -= BYTES_LONG) {
> + last = next;
> + next = s.as_ulong[1];
> +
> + d.as_ulong[0] = last >> (distance * 8) |
> + next << ((BYTES_LONG - distance) * 8);
> +
> + d.as_ulong++;
> + s.as_ulong++;
> + }
> +
> + /* Restore s with the original offset. */
> + s.as_u8 += distance;
> + } else {
> + /*
> + * 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.as_ulong++ = *s.as_ulong++;
> + }
> +
> +copy_remainder:
> + while (count--)
> + *d.as_u8++ = *s.as_u8++;
> +
> + return dest;
> +}
> +EXPORT_SYMBOL(__memcpy);
> +
> +void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);
> +EXPORT_SYMBOL(memcpy);
> --
> 2.31.1
>
--
Best Regards
Guo Ren
ML: https://lore.kernel.org/linux-csky/
On Thu, Sep 30, 2021 at 3:25 AM Guo Ren <[email protected]> wrote:
>
> On Thu, Sep 30, 2021 at 1:22 AM Matteo Croce <[email protected]> wrote:
> >
> > From: Matteo Croce <[email protected]>
> >
> > 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 <[email protected]>
> > Reported-by: kernel test robot <[email protected]>
> > ---
> > 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 | 90 ++++++++++++++++++++++++++
> > 5 files changed, 97 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
> What's the problem with the -O3 & -Os? If the user uses
> CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 that will cause bad performance
> for memcpy?
> Seems asm version is more compatible?
>
> > #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..bfc912ee23f8
> > --- /dev/null
> > +++ b/arch/riscv/lib/string.c
> > @@ -0,0 +1,90 @@
> > +// 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 BYTES_LONG sizeof(long)
> > +#define WORD_MASK (BYTES_LONG - 1)
> > +#define MIN_THRESHOLD (BYTES_LONG * 2)
> > +
> > +/* convenience union to avoid cast between different pointer types */
> > +union types {
> > + u8 *as_u8;
> > + unsigned long *as_ulong;
> > + uintptr_t as_uptr;
> > +};
> > +
> > +union const_types {
> > + const u8 *as_u8;
> > + unsigned long *as_ulong;
> > + uintptr_t as_uptr;
> > +};
> > +
> > +void *__memcpy(void *dest, const void *src, size_t count)
> How about using __attribute__((optimize("-O2"))) here to replace your
> previous "#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE"?
>
> > +{
> > + union const_types s = { .as_u8 = src };
> > + union types d = { .as_u8 = dest };
> > + int distance = 0;
> > +
> > + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
> > + if (count < MIN_THRESHOLD)
> > + goto copy_remainder;
> > +
> > + /* Copy a byte at time until destination is aligned. */
> > + for (; d.as_uptr & WORD_MASK; count--)
> > + *d.as_u8++ = *s.as_u8++;
> > +
> > + distance = s.as_uptr & WORD_MASK;
> > + }
> > +
> > + if (distance) {
> > + unsigned long last, next;
> > +
> > + /*
> > + * s is distance bytes ahead of d, and d just reached
> > + * the alignment boundary. Move s backward to word align it
> > + * and shift data to compensate for distance, in order to do
> > + * word-by-word copy.
> > + */
> > + s.as_u8 -= distance;
> > +
> > + next = s.as_ulong[0];
> > + for (; count >= BYTES_LONG; count -= BYTES_LONG) {
> > + last = next;
> > + next = s.as_ulong[1];
> > +
> > + d.as_ulong[0] = last >> (distance * 8) |
> > + next << ((BYTES_LONG - distance) * 8);
> > +
> > + d.as_ulong++;
> > + s.as_ulong++;
> > + }
> > +
> > + /* Restore s with the original offset. */
> > + s.as_u8 += distance;
> > + } else {
> > + /*
> > + * 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.as_ulong++ = *s.as_ulong++;
> > + }
> > +
> > +copy_remainder:
> > + while (count--)
> > + *d.as_u8++ = *s.as_u8++;
> > +
> > + return dest;
> > +}
> > +EXPORT_SYMBOL(__memcpy);
> > +
> > +void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);
> > +EXPORT_SYMBOL(memcpy);
> > --
> > 2.31.1
> >
>
>
> --
> Best Regards
> Guo Ren
>
> ML: https://lore.kernel.org/linux-csky/
If CONFIG_CC_OPTIMIZE_FOR_SIZE I fallback to the generic
implementations, which are very small.
It's just an optimization to save more space when -Os is used.
CC_OPTIMIZE_FOR_PERFORMANCE_O3 is ARC specific.
Regards,
--
per aspera ad upstream
On 9/29/21 6:36 PM, Matteo Croce wrote:
> On Thu, Sep 30, 2021 at 3:25 AM Guo Ren <[email protected]> wrote:
>>
>> On Thu, Sep 30, 2021 at 1:22 AM Matteo Croce <[email protected]> wrote:
>>>
>>> From: Matteo Croce <[email protected]>
>>>
>>> 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 <[email protected]>
>>> Reported-by: kernel test robot <[email protected]>
>>> ---
>>> 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 | 90 ++++++++++++++++++++++++++
>>> 5 files changed, 97 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
>> What's the problem with the -O3 & -Os? If the user uses
>> CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE_O3 that will cause bad performance
>> for memcpy?
>> Seems asm version is more compatible?
>>
>>> #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..bfc912ee23f8
>>> --- /dev/null
>>> +++ b/arch/riscv/lib/string.c
>>> @@ -0,0 +1,90 @@
>>> +// 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 BYTES_LONG sizeof(long)
>>> +#define WORD_MASK (BYTES_LONG - 1)
>>> +#define MIN_THRESHOLD (BYTES_LONG * 2)
>>> +
>>> +/* convenience union to avoid cast between different pointer types */
>>> +union types {
>>> + u8 *as_u8;
>>> + unsigned long *as_ulong;
>>> + uintptr_t as_uptr;
>>> +};
>>> +
>>> +union const_types {
>>> + const u8 *as_u8;
>>> + unsigned long *as_ulong;
>>> + uintptr_t as_uptr;
>>> +};
>>> +
>>> +void *__memcpy(void *dest, const void *src, size_t count)
>> How about using __attribute__((optimize("-O2"))) here to replace your
>> previous "#ifdef CONFIG_CC_OPTIMIZE_FOR_PERFORMANCE"?
>>
>>> +{
>>> + union const_types s = { .as_u8 = src };
>>> + union types d = { .as_u8 = dest };
>>> + int distance = 0;
>>> +
>>> + if (!IS_ENABLED(CONFIG_HAVE_EFFICIENT_UNALIGNED_ACCESS)) {
>>> + if (count < MIN_THRESHOLD)
>>> + goto copy_remainder;
>>> +
>>> + /* Copy a byte at time until destination is aligned. */
>>> + for (; d.as_uptr & WORD_MASK; count--)
>>> + *d.as_u8++ = *s.as_u8++;
>>> +
>>> + distance = s.as_uptr & WORD_MASK;
>>> + }
>>> +
>>> + if (distance) {
>>> + unsigned long last, next;
>>> +
>>> + /*
>>> + * s is distance bytes ahead of d, and d just reached
>>> + * the alignment boundary. Move s backward to word align it
>>> + * and shift data to compensate for distance, in order to do
>>> + * word-by-word copy.
>>> + */
>>> + s.as_u8 -= distance;
>>> +
>>> + next = s.as_ulong[0];
>>> + for (; count >= BYTES_LONG; count -= BYTES_LONG) {
>>> + last = next;
>>> + next = s.as_ulong[1];
>>> +
>>> + d.as_ulong[0] = last >> (distance * 8) |
>>> + next << ((BYTES_LONG - distance) * 8);
>>> +
>>> + d.as_ulong++;
>>> + s.as_ulong++;
>>> + }
>>> +
>>> + /* Restore s with the original offset. */
>>> + s.as_u8 += distance;
>>> + } else {
>>> + /*
>>> + * 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.as_ulong++ = *s.as_ulong++;
>>> + }
>>> +
>>> +copy_remainder:
>>> + while (count--)
>>> + *d.as_u8++ = *s.as_u8++;
>>> +
>>> + return dest;
>>> +}
>>> +EXPORT_SYMBOL(__memcpy);
>>> +
>>> +void *memcpy(void *dest, const void *src, size_t count) __weak __alias(__memcpy);
>>> +EXPORT_SYMBOL(memcpy);
>>> --
>>> 2.31.1
>>>
>>
>>
>> --
>> Best Regards
>> Guo Ren
>>
>> ML: https://lore.kernel.org/linux-csky/
>
> If CONFIG_CC_OPTIMIZE_FOR_SIZE I fallback to the generic
> implementations, which are very small.
> It's just an optimization to save more space when -Os is used.
>
> CC_OPTIMIZE_FOR_PERFORMANCE_O3 is ARC specific.
It is not. Its just that for ARC I've used -O3 as default. Historically
for compilers at the time some architecture had issues with -O3 builds
and/or compiler would inline more. But nothing in -O3 is specific to ARC.
BTW off topic (but relevant to this patchset), I strongly feel that
routines like memset/memcpy are better coded in assembly for really
water tight instruction scheduling and ease of further optimizing (e.g.
use of CMO.zero etc as experimented by Philipp). What is blocking you
from optimizing the asm version ? You are leaving the fate of these
critical routines in the hand of compiler - this can lead to performance
shenanigans on a big gcc upgrade.
-Vineet
...
> BTW off topic (but relevant to this patchset), I strongly feel that
> routines like memset/memcpy are better coded in assembly for really
> water tight instruction scheduling and ease of further optimizing (e.g.
> use of CMO.zero etc as experimented by Philipp). What is blocking you
> from optimizing the asm version ? You are leaving the fate of these
> critical routines in the hand of compiler - this can lead to performance
> shenanigans on a big gcc upgrade.
You also need to worry about the cost of short transfers.
A few cycles there could have a much bigger difference
that something that speeds up long transfers.
Short ones are likely to be fairly common.
I doubt the loop unrolling optimisation in gcc is actually
any good for loops that might be done a few times.
Fortunately the kernel doesn't get 'hit by' gcc unrolling
loops into the AVX instructions.
The setup costs for that (and I-cache footprint) are horrid.
Although I suspect it is that optimisation that 'broke'
code that used misaligned pointers on overlapping data.
It is a general problem with the 'one size fits all' memcpy().
David
-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Hi!
> From: Matteo Croce <[email protected]>
>
> 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
>
> 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
That's really quite cool. Could you see if it is your "optimized
unaligned" copy doing the difference?>
+/* convenience union to avoid cast between different pointer types */
> +union types {
> + u8 *as_u8;
> + unsigned long *as_ulong;
> + uintptr_t as_uptr;
> +};
> +
> +union const_types {
> + const u8 *as_u8;
> + unsigned long *as_ulong;
> + uintptr_t as_uptr;
> +};
Missing consts here?
Plus... this is really "interesting" coding style. I'd just use casts
in kernel.
Regards, Pavel
--
http://www.livejournal.com/~pavelmachek
On Fri, Oct 1, 2021 at 1:23 PM Pavel Machek <[email protected]> wrote:
>
> Hi!
>
> > From: Matteo Croce <[email protected]>
> >
> > 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
> >
> > 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
>
> That's really quite cool. Could you see if it is your "optimized
> unaligned" copy doing the difference?>
>
> +/* convenience union to avoid cast between different pointer types */
> > +union types {
> > + u8 *as_u8;
> > + unsigned long *as_ulong;
> > + uintptr_t as_uptr;
> > +};
> > +
> > +union const_types {
> > + const u8 *as_u8;
> > + unsigned long *as_ulong;
> > + uintptr_t as_uptr;
> > +};
>
> Missing consts here?
>
> Plus... this is really "interesting" coding style. I'd just use casts
> in kernel.
>
Yes, the one for as_ulong is missing.
By using casts I had to use too many of them, making repeated
assignments in every function.
This is basically the same, with less code :)
Cheers,
--
per aspera ad upstream