[PATCH v7 2/2] RISC-V: add riscv vector support for memcpy

[Anton Blanchard]

Hi,

On Fri, Feb 21, 2025 at 8:57 PM <daichengrong@iscas.ac.cn> wrote:
> From: daichengrong <daichengrong@iscas.ac.cn>
>
> Change in v7:
>    update dl_hwcap support using kernel header
>    update rvv memcpy compile with option,+v
>    delete optimization for small lengths

I tested this again on our upcoming Tenstorrent Ascalon CPU and (as
before) it's a 3x speedup on long lengths, a clear improvement for
everything 16 bytes onwards and no significant regressions on lengths
less than 16 bytes.

Tested-by: Anton Blanchard <antonb@tenstorrent.com>

Anton

> Change in v6:
>    Optimize the RVV memcpy for small lengths less than VLEN/8 bytes
>
> Changes in v5:
>    check ifunc-impl-list memcpy vector support with by dl_hwcap
>
> Changes in v4:
>    update rvv memcpy support by compiler
>    check whether rvv enabled by dl_hwcap
>
> Changes in v2:
>    delete size-0 branch
> ---
>  sysdeps/riscv/multiarch/memcpy_vector.S       | 37 +++++++++++++++++++
>  .../unix/sysv/linux/riscv/multiarch/Makefile  |  6 +++
>  .../linux/riscv/multiarch/ifunc-impl-list.c   | 14 +++++++
>  .../unix/sysv/linux/riscv/multiarch/memcpy.c  |  8 ++++
>  4 files changed, 65 insertions(+)
>  create mode 100644 sysdeps/riscv/multiarch/memcpy_vector.S
>
> diff --git a/sysdeps/riscv/multiarch/memcpy_vector.S b/sysdeps/riscv/multiarch/memcpy_vector.S
> new file mode 100644
> index 0000000000..eaf28aaf6d
> --- /dev/null
> +++ b/sysdeps/riscv/multiarch/memcpy_vector.S
> @@ -0,0 +1,37 @@
> +/* memcpy for RISC-V Vector.
> +   Copyright (C) 2024-2025 Free Software Foundation, Inc.
> +   This file is part of the GNU C Library.
> +
> +   The GNU C Library is free software; you can redistribute it and/or
> +   modify it under the terms of the GNU Lesser General Public
> +   License as published by the Free Software Foundation; either
> +   version 2.1 of the License, or (at your option) any later version.
> +
> +   The GNU C Library is distributed in the hope that it will be useful,
> +   but WITHOUT ANY WARRANTY; without even the implied warranty of
> +   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
> +   Lesser General Public License for more details.
> +
> +   You should have received a copy of the GNU Lesser General Public
> +   License along with the GNU C Library; if not, see
> +   <https://www.gnu.org/licenses/>.  */
> +
> +
> +#include <sysdep.h>
> +#include <sys/asm.h>
> +
> +ENTRY (__memcpy_vector)
> +.option push
> +.option arch, +v
> +    mv     a6, a0
> +L(loop):
> +    vsetvli a3,a2,e8,m8,ta,ma
> +    vle8.v  v8,(a1)
> +    vse8.v  v8,(a6)
> +    add     a1,a1,a3
> +    sub     a2,a2,a3
> +    add     a6,a6,a3
> +    bnez    a2,L(loop)
> +    ret
> +.option pop
> +END (__memcpy_vector)
> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
> index fcef5659d4..478338006b 100644
> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/Makefile
> @@ -5,5 +5,11 @@ sysdep_routines += \
>    memcpy_noalignment \
>    # sysdep_routines
>
> +ifeq ($(have-gcc-riscv-rvv),yes)
> +sysdep_routines += \
> +  memcpy_vector \
> +  # rvv sysdep_routines
> +endif
> +
>  CFLAGS-memcpy_noalignment.c += -mno-strict-align
>  endif
> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
> index 1c1deca8f6..26f3376d23 100644
> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/ifunc-impl-list.c
> @@ -19,6 +19,8 @@
>  #include <ifunc-impl-list.h>
>  #include <string.h>
>  #include <sys/hwprobe.h>
> +#include <ldsodefs.h>
> +#include <asm/hwcap.h>
>
>  size_t
>  __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
> @@ -27,6 +29,9 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
>    size_t i = max;
>
>    bool fast_unaligned = false;
> +#if defined(HAVE_RISCV_ASM_VECTOR_SUPPORT)
> +  bool rvv_ext = false;
> +#endif
>
>    struct riscv_hwprobe pair = { .key = RISCV_HWPROBE_KEY_CPUPERF_0 };
>    if (__riscv_hwprobe (&pair, 1, 0, NULL, 0) == 0
> @@ -34,7 +39,16 @@ __libc_ifunc_impl_list (const char *name, struct libc_ifunc_impl *array,
>            == RISCV_HWPROBE_MISALIGNED_FAST)
>      fast_unaligned = true;
>
> +#if defined(HAVE_RISCV_ASM_VECTOR_SUPPORT)
> +  if (GLRO(dl_hwcap) & COMPAT_HWCAP_ISA_V)
> +    rvv_ext = true;
> +#endif
> +
>    IFUNC_IMPL (i, name, memcpy,
> +#if defined(HAVE_RISCV_ASM_VECTOR_SUPPORT)
> +             IFUNC_IMPL_ADD (array, i, memcpy, rvv_ext,
> +                             __memcpy_vector)
> +#endif
>               IFUNC_IMPL_ADD (array, i, memcpy, fast_unaligned,
>                               __memcpy_noalignment)
>               IFUNC_IMPL_ADD (array, i, memcpy, 1, __memcpy_generic))
> diff --git a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> index 8544f5402a..4bedd21866 100644
> --- a/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> +++ b/sysdeps/unix/sysv/linux/riscv/multiarch/memcpy.c
> @@ -27,16 +27,24 @@
>  # include <ifunc-init.h>
>  # include <riscv-ifunc.h>
>  # include <sys/hwprobe.h>
> +# include <asm/hwcap.h>
>
>  extern __typeof (__redirect_memcpy) __libc_memcpy;
>
>  extern __typeof (__redirect_memcpy) __memcpy_generic attribute_hidden;
>  extern __typeof (__redirect_memcpy) __memcpy_noalignment attribute_hidden;
> +extern __typeof (__redirect_memcpy) __memcpy_vector attribute_hidden;
>
>  static inline __typeof (__redirect_memcpy) *
>  select_memcpy_ifunc (uint64_t dl_hwcap, __riscv_hwprobe_t hwprobe_func)
>  {
>    unsigned long long int v;
> +
> +#if defined(HAVE_RISCV_ASM_VECTOR_SUPPORT)
> +  if (dl_hwcap & COMPAT_HWCAP_ISA_V)
> +    return __memcpy_vector;
> +#endif
> +
>    if (__riscv_hwprobe_one (hwprobe_func, RISCV_HWPROBE_KEY_CPUPERF_0, &v) == 0
>        && (v & RISCV_HWPROBE_MISALIGNED_MASK) == RISCV_HWPROBE_MISALIGNED_FAST)
>      return __memcpy_noalignment;
> --
> 2.25.1
>
>