Re: [PATCH 1/3] riscv: optimized memcpy

[Guo Ren <guoren@kernel.org>]

Hi Matteo,

Have you tried Glibc generic implementation code?
ref: https://lore.kernel.org/linux-arch/20190629053641.3iBfk9-I_D29cDp9yJnIdIg7oMtHNZlDmhLQPTumhEc@z/#t

If Glibc codes have the same performance in your hardware, then you
could give a generic implementation first.

The current Linux generic implementation is so simple in lib/string.c:
#ifndef __HAVE_ARCH_MEMCPY
/**
 * memcpy - Copy one area of memory to another
 * @dest: Where to copy to
 * @src: Where to copy from
 * @count: The size of the area.
 *
 * You should not use this function to access IO space, use memcpy_toio()
 * or memcpy_fromio() instead.
 */
void *memcpy(void *dest, const void *src, size_t count)
{
        char *tmp = dest;
        const char *s = src;

        while (count--)
                *tmp++ = *s++;
        return dest;
}
EXPORT_SYMBOL(memcpy);
#endif

On Tue, Jun 15, 2021 at 10:42 AM Matteo Croce
<mcroce@linux.microsoft.com> wrote:
>
> From: Matteo Croce <mcroce@microsoft.com>
>
> 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@microsoft.com>
> ---
>  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..525f9ee25a74
> --- /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>
> +
> +/* size below a classic byte at time copy is done */
> +#define MIN_THRESHOLD 64
> +
> +/* convenience types 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 *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
>


-- 
Best Regards
 Guo Ren

ML: https://lore.kernel.org/linux-csky/