[PATCH] riscv: Optimize memset
Andrew Jones
ajones at ventanamicro.com
Fri May 5 04:54:56 PDT 2023
Please don't post patches as attachments.
> From: zhangfei <zhangfei at nj.iscas.ac.cn>
> Date: Fri, 5 May 2023 14:58:35 +0800
> Subject: [PATCH] riscv: Optimize memset
>
> This patch has been optimized for memset data sizes less than 16 bytes.
> Compared to byte by byte storage, significant performance improvement has been achieved.
>
> Signed-off-by: Fei Zhang <zhangfei at nj.iscas.ac.cn>
> ---
> arch/riscv/lib/memset.S | 33 ++++++++++++++++++++++++++++++---
> 1 file changed, 30 insertions(+), 3 deletions(-)
>
> diff --git a/arch/riscv/lib/memset.S b/arch/riscv/lib/memset.S
> index 34c5360c6705..0967bdf86bd6 100644
> --- a/arch/riscv/lib/memset.S
> +++ b/arch/riscv/lib/memset.S
> @@ -105,9 +105,36 @@ WEAK(memset)
> beqz a2, 6f
> add a3, t0, a2
> 5:
> - sb a1, 0(t0)
> - addi t0, t0, 1
> - bltu t0, a3, 5b
> + sb a1, 0(t0)
> + sb a1, -1(a3)
> + li a4, 2
> + bgeu a4, a2, 6f
> +
> + sb a1, 1(t0)
> + sb a1, 2(t0)
> + sb a1, -2(a3)
> + sb a1, -3(a3)
> + li a4, 6
> + bgeu a4, a2, 6f
> +
> + sb a1, 3(t0)
> + sb a1, -4(a3)
> + li a4, 8
> + bgeu a4, a2, 6f
Why is this check here?
> +
> + sb a1, 4(t0)
> + sb a1, -5(a3)
> + li a4, 10
> + bgeu a4, a2, 6f
And this one?
After the check of a2 against 6 above we know that offsets 6(t0)
and -7(a3) are safe. Are we trying to avoid too may redundant
stores with these additional checks?
> +
> + sb a1, 5(t0)
> + sb a1, 6(t0)
> + sb a1, -6(a3)
> + sb a1, -7(a3)
> + li a4, 14
> + bgeu a4, a2, 6f
> +
> + sb a1, 7(t0)
> 6:
> ret
> END(__memset)
> --
> 2.33.0
The indent of the new code doesn't match the old. I'd prefer we cleanup
the old first, though. Please repost [1] as a first patch of a two-patch
patch series, where yours is the second and matches the new formatting
that [1] uses.
[1] https://lore.kernel.org/all/20221027130247.31634-8-ajones@ventanamicro.com/
Thanks,
Drew
On Fri, May 05, 2023 at 04:43:44PM +0800, 张飞 wrote:
>
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