[PATCH] riscv:lib: optimize memcmp with ld insn

[Conor.Dooley at microchip.com]

On 31/08/2022 14:07, Yipeng Zou wrote:
> riscv:lib: optimize memcmp with ld insn

Minor nit: "riscv: lib:

> EXTERNAL EMAIL: Do not click links or open attachments unless you know the content is safe
> 
> Currently memcmp was implemented in c code(lib/string.c), which compare
> memory per byte.
> 
> This patch use ld insn compare memory per word to improve. From the test
> Results, this will take several times optimized.

Hey Yipeng,
Could you share some more information about the tests you did?
The test results showing the % improvement would be nice :)
Thanks,
Conor.

> 
> Signed-off-by: Yipeng Zou <zouyipeng at huawei.com>
> ---
>   arch/riscv/include/asm/string.h |  3 ++
>   arch/riscv/lib/Makefile         |  1 +
>   arch/riscv/lib/memcmp.S         | 59 +++++++++++++++++++++++++++++++++
>   3 files changed, 63 insertions(+)
>   create mode 100644 arch/riscv/lib/memcmp.S
> 
> diff --git a/arch/riscv/include/asm/string.h b/arch/riscv/include/asm/string.h
> index 909049366555..3337b43d3803 100644
> --- a/arch/riscv/include/asm/string.h
> +++ b/arch/riscv/include/asm/string.h
> @@ -18,6 +18,9 @@ extern asmlinkage void *__memcpy(void *, const void *, size_t);
>   #define __HAVE_ARCH_MEMMOVE
>   extern asmlinkage void *memmove(void *, const void *, size_t);
>   extern asmlinkage void *__memmove(void *, const void *, size_t);
> +#define __HAVE_ARCH_MEMCMP
> +extern int memcmp(const 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/lib/Makefile b/arch/riscv/lib/Makefile
> index 25d5c9664e57..70773bf0c471 100644
> --- a/arch/riscv/lib/Makefile
> +++ b/arch/riscv/lib/Makefile
> @@ -3,6 +3,7 @@ lib-y                   += delay.o
>   lib-y                  += memcpy.o
>   lib-y                  += memset.o
>   lib-y                  += memmove.o
> +lib-y                  += memcmp.o
>   lib-$(CONFIG_MMU)      += uaccess.o
>   lib-$(CONFIG_64BIT)    += tishift.o
> 
> diff --git a/arch/riscv/lib/memcmp.S b/arch/riscv/lib/memcmp.S
> new file mode 100644
> index 000000000000..83af1c433e6f
> --- /dev/null
> +++ b/arch/riscv/lib/memcmp.S
> @@ -0,0 +1,59 @@
> +/* SPDX-License-Identifier: GPL-2.0-only */
> +/*
> + * Copyright (C) 2022 zouyipeng at huawei.com
> + */
> +#include <linux/linkage.h>
> +#include <asm-generic/export.h>
> +#include <asm/asm.h>
> +
> +/* argrments:
> +* a0: addr0
> +* a1: addr1
> +* a2: size
> +*/
> +#define addr0  a0
> +#define addr1  a1
> +#define limit  a2
> +
> +#define data0  a3
> +#define data1  a4
> +#define tmp    t3
> +#define aaddr  t4
> +#define return a0
> +
> +/* load and compare */
> +.macro LD_CMP op d0 d1 a0 a1 offset
> +       \op \d0, 0(\a0)
> +       \op \d1, 0(\a1)
> +       addi \a0, \a0, \offset
> +       addi \a1, \a1, \offset
> +       sub tmp, \d0, \d1
> +.endm
> +
> +ENTRY(memcmp)
> +       /* test limit aligend with SZREG */
> +       andi tmp, limit, SZREG - 1
> +       /* load tail */
> +       add aaddr, addr0, limit
> +       sub aaddr, aaddr, tmp
> +       add limit, addr0, limit
> +
> +.LloopWord:
> +       sltu tmp, addr0, aaddr
> +       beqz tmp, .LloopByte
> +
> +       LD_CMP REG_L data0 data1 addr0 addr1 SZREG
> +       beqz tmp, .LloopWord
> +       j .Lreturn
> +
> +.LloopByte:
> +       sltu tmp, addr0, limit
> +       beqz tmp, .Lreturn
> +
> +       LD_CMP lbu data0 data1 addr0 addr1 1
> +       beqz tmp, .LloopByte
> +.Lreturn:
> +       mv return, tmp
> +       ret
> +END(memcmp)
> +EXPORT_SYMBOL(memcmp);
> --
> 2.17.1
>