On Thu, Sep 30, 2021 at 1:22 AM Matteo Croce <mcroce@xxxxxxxxxxxxxxxxxxx> wrote:
>
> 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>
> Reported-by: kernel test robot <lkp@xxxxxxxxx>
> ---
> 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/
