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From:   Matteo Croce <mcroce@linux.microsoft.com>
Date:   Wed, 16 Jun 2021 20:52:13 +0200
Message-ID: <CAFnufp1OHdRd-tbB+Hi0UnXARtxGPdkK6MJktnaNCNt65d3Oew@mail.gmail.com>
Subject: Re: [PATCH 1/3] riscv: optimized memcpy
To:     Guo Ren <guoren@kernel.org>
Cc:     linux-riscv <linux-riscv@lists.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
        linux-arch <linux-arch@vger.kernel.org>,
        Paul Walmsley <paul.walmsley@sifive.com>,
        Palmer Dabbelt <palmer@dabbelt.com>,
        Albert Ou <aou@eecs.berkeley.edu>,
        Atish Patra <atish.patra@wdc.com>,
        Emil Renner Berthing <kernel@esmil.dk>,
        Akira Tsukamoto <akira.tsukamoto@gmail.com>,
        Drew Fustini <drew@beagleboard.org>,
        Bin Meng <bmeng.cn@gmail.com>
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On Wed, Jun 16, 2021 at 1:46 PM Guo Ren <guoren@kernel.org> wrote:
>
> 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.
>

Hi,

I had a look, it seems that it's a C unrolled version with the
'register' keyword.
The same one was already merged in nios2:
https://elixir.bootlin.com/linux/latest/source/arch/nios2/lib/memcpy.c#L68

I copied _wordcopy_fwd_aligned() from Glibc, and I have a very similar
result of the other versions:

[  563.359126] Strings selftest: memcpy(src+7, dst+7): 257 Mb/s

Regards,
-- 
per aspera ad upstream