linux-kernel - Re: [PATCH] powerpc/32: Optimise __csum

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Date:   Thu, 24 May 2018 14:58:40 -0500
From:   Segher Boessenkool <segher@...nel.crashing.org>
To:     Christophe Leroy <christophe.leroy@....fr>
Cc:     Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org
Subject: Re: [PATCH] powerpc/32: Optimise __csum_partial()

On Thu, May 24, 2018 at 11:22:27AM +0000, Christophe Leroy wrote:
> Improve __csum_partial by interleaving loads and adds.
> 
> On a 8xx, it brings neither improvement nor degradation.
> On a 83xx, it brings a 25% improvement.

Thanks!  Looks fine to me.

> Signed-off-by: Christophe Leroy <christophe.leroy@....fr>

Reviewed-by: Segher Boessenkool <segher@...nel.crashing.org>

> ---
>  arch/powerpc/lib/checksum_32.S | 13 +++++++++++--
>  1 file changed, 11 insertions(+), 2 deletions(-)
> 
> diff --git a/arch/powerpc/lib/checksum_32.S b/arch/powerpc/lib/checksum_32.S
> index d2238ea82209..aa224069f93a 100644
> --- a/arch/powerpc/lib/checksum_32.S
> +++ b/arch/powerpc/lib/checksum_32.S
> @@ -47,16 +47,25 @@ _GLOBAL(__csum_partial)
>  	bdnz	2b
>  21:	srwi.	r6,r4,4		/* # blocks of 4 words to do */
>  	beq	3f
> +	lwz	r0,4(r3)
>  	mtctr	r6
> -22:	lwz	r0,4(r3)
>  	lwz	r6,8(r3)
> +	adde	r5,r5,r0
>  	lwz	r7,12(r3)
> +	adde	r5,r5,r6
>  	lwzu	r8,16(r3)
> +	adde	r5,r5,r7
> +	bdz	23f
> +22:	lwz	r0,4(r3)
> +	adde	r5,r5,r8
> +	lwz	r6,8(r3)
>  	adde	r5,r5,r0
> +	lwz	r7,12(r3)
>  	adde	r5,r5,r6
> +	lwzu	r8,16(r3)
>  	adde	r5,r5,r7
> -	adde	r5,r5,r8
>  	bdnz	22b
> +23:	adde	r5,r5,r8
>  3:	andi.	r0,r4,2
>  	beq+	4f
>  	lhz	r0,4(r3)
> -- 
> 2.13.3