linux-kernel - Re: [Bug fix]mips 64bits checksum error -- csum_tcpudp

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Date:   Thu, 26 Jan 2017 07:57:49 -0800
From:   Alexander Duyck <alexander.duyck@...il.com>
To:     Mark Zhang <bomb.zhang@...il.com>
Cc:     Ralf Baechle <ralf@...ux-mips.org>,
        David Miller <davem@...emloft.net>,
        Alexander Duyck <aduyck@...antis.com>,
        linux-mips@...ux-mips.org,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [Bug fix]mips 64bits checksum error -- csum_tcpudp_nofold

On Wed, Jan 25, 2017 at 6:33 PM, Mark Zhang <bomb.zhang@...il.com> wrote:
> Hi Alex,
>
>     Thanks for your reply.
>     I tested your correction. The result is correct.
>     The C language will cause this function(csum_tcpudp_nofold) become
> 176 MIPS instructions. The assemble code is 150 MIPS instruction.
>     If the MIPS CPU is running as 1GHz, C language cause more 60 nano
> seconds during send/receive each tcp/udp packet. I'm not sure whether
> it will cause any negative result if the frequency of CPU was lower.
> MIPS arch is usually used in networking equipments.
>     I think Ralf's correction is better.
>
>     - Mark
>
> Signed-off-by: Ralf Baechle <ralf@...ux-mips.org>
>
>  arch/mips/include/asm/checksum.h | 2 ++
>  1 file changed, 2 insertions(+)
>
> diff --git a/arch/mips/include/asm/checksum.h b/arch/mips/include/asm/checksum.h
> index 5c585c5..08b6ba3 100644
> --- a/arch/mips/include/asm/checksum.h
> +++ b/arch/mips/include/asm/checksum.h
> @@ -186,7 +186,9 @@ static inline __wsum csum_tcpudp_nofold(__be32 saddr,
>         "       daddu   %0, %4          \n"
>         "       dsll32  $1, %0, 0       \n"
>         "       daddu   %0, $1          \n"
> +       "       sltu    $1, %0, $1      \n"
>         "       dsra32  %0, %0, 0       \n"
> +       "       daddu   %0, $1          \n"
>  #endif
>         "       .set    pop"
>         : "=r" (sum)
>

This looks good to me.

Acked-by: Alexander Duyck <alexander.h.duyck@...el.com>