linux-kernel - Re: [PATCH] microblaze: speedup for word-aligned memcpys

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Message-ID: <4BC42650.5030305@monstr.eu>
Date:	Tue, 13 Apr 2010 10:07:44 +0200
From:	Michal Simek <monstr@...str.eu>
To:	"Steven J. Magnani" <steve@...idescorp.com>
CC:	microblaze-uclinux@...e.uq.edu.au, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] microblaze: speedup for word-aligned memcpys

Steven J. Magnani wrote:
> memcpy performance was measured on a noMMU system having a barrel shifter, 
> 4K caches, and 32-byte write-through cachelines. In this environment, 
> copying word-aligned data in word-sized chunks appears to be about 3% more 
> efficient on packet-sized buffers (1460 bytes) than copying in cacheline-sized 
> chunks.
> 
> Skip to word-based copying when buffers are both word-aligned.
> 
> Signed-off-by: Steven J. Magnani <steve@...idescorp.com>

I added this patch to next branch and I will keep it there for now.

1. I agree that we need several patches like this.
2. The improvement could be there and likely it is but 3% improvement 
could be caused for different reason.
3. There is necessary to measure it on several hw design and cache 
configurations to be sure that your expectation is correct.
4. The best will be to monitoring cache behavior but currently there is 
no any tool which could easily help us with it.

I will talk to xilinx how to monitoring it.

Thanks,
Michal


> ---
> diff -uprN a/arch/microblaze/lib/fastcopy.S b/arch/microblaze/lib/fastcopy.S
> --- a/arch/microblaze/lib/fastcopy.S	2010-04-09 21:52:36.000000000 -0500
> +++ b/arch/microblaze/lib/fastcopy.S	2010-04-12 15:37:44.000000000 -0500
> @@ -69,37 +69,13 @@ a_dalign_done:
>  	blti	r4, a_block_done
>  
>  a_block_xfer:
> -	andi	r4, r7, 0xffffffe0	/* n = c & ~31 */
> -	rsub	r7, r4, r7		/* c = c - n */
> -
>  	andi	r9, r6, 3		/* t1 = s & 3 */
> -	/* if temp != 0, unaligned transfers needed */
> -	bnei	r9, a_block_unaligned
> -
> -a_block_aligned:
> -	lwi	r9, r6, 0		/* t1 = *(s + 0) */
> -	lwi	r10, r6, 4		/* t2 = *(s + 4) */
> -	lwi	r11, r6, 8		/* t3 = *(s + 8) */
> -	lwi	r12, r6, 12		/* t4 = *(s + 12) */
> -	swi	r9, r5, 0		/* *(d + 0) = t1 */
> -	swi	r10, r5, 4		/* *(d + 4) = t2 */
> -	swi	r11, r5, 8		/* *(d + 8) = t3 */
> -	swi	r12, r5, 12		/* *(d + 12) = t4 */
> -	lwi	r9, r6, 16		/* t1 = *(s + 16) */
> -	lwi	r10, r6, 20		/* t2 = *(s + 20) */
> -	lwi	r11, r6, 24		/* t3 = *(s + 24) */
> -	lwi	r12, r6, 28		/* t4 = *(s + 28) */
> -	swi	r9, r5, 16		/* *(d + 16) = t1 */
> -	swi	r10, r5, 20		/* *(d + 20) = t2 */
> -	swi	r11, r5, 24		/* *(d + 24) = t3 */
> -	swi	r12, r5, 28		/* *(d + 28) = t4 */
> -	addi	r6, r6, 32		/* s = s + 32 */
> -	addi	r4, r4, -32		/* n = n - 32 */
> -	bneid	r4, a_block_aligned	/* while (n) loop */
> -	addi	r5, r5, 32		/* d = d + 32 (IN DELAY SLOT) */
> -	bri	a_block_done
> +	/* if temp == 0, everything is word-aligned */
> +	beqi	r9, a_word_xfer
>  
>  a_block_unaligned:
> +	andi	r4, r7, 0xffffffe0	/* n = c & ~31 */
> +	rsub	r7, r4, r7		/* c = c - n */
>  	andi	r8, r6, 0xfffffffc	/* as = s & ~3 */
>  	add	r6, r6, r4		/* s = s + n */
>  	lwi	r11, r8, 0		/* h = *(as + 0) */
> 


-- 
Michal Simek, Ing. (M.Eng)
w: www.monstr.eu p: +42-0-721842854
Maintainer of Linux kernel 2.6 Microblaze Linux - http://www.monstr.eu/fdt/
Microblaze U-BOOT custodian
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