linux-kernel - RE: [PATCH RFC 1/2 ] [x86] Optimize copy-page by reducing impact from HW prefetch

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Date:	Wed, 29 Jun 2011 09:24:09 +0800
From:	"Ma, Ling" <ling.ma@...el.com>
To:	"Ma, Ling" <ling.ma@...el.com>, "mingo@...e.hu" <mingo@...e.hu>
CC:	"hpa@...or.com" <hpa@...or.com>,
	"tglx@...utronix.de" <tglx@...utronix.de>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH RFC 1/2 ] [x86] Optimize copy-page by reducing impact
 from HW prefetch

This patch subject should be  [PATCH RFC 2/2 ] [x86] Optimize copy-page by reducing impact from HW prefetch,
I will change it in next version with your comments.

Thanks
Ling

> -----Original Message-----
> From: Ma, Ling
> Sent: Wednesday, June 29, 2011 6:37 AM
> To: mingo@...e.hu
> Cc: hpa@...or.com; tglx@...utronix.de; linux-kernel@...r.kernel.org; Ma,
> Ling
> Subject: [PATCH RFC 1/2 ] [x86] Optimize copy-page by reducing impact
> from HW prefetch
> 
> From: Ma Ling <ling.ma@...el.com>
> 
> Program's temporal & spatial locality introduce cache unit to overcome
> the processor-memory performance gap, hardware prefetch is very
> important
> to improve performance by reducing cache miss. Modern CPU micro-
> architecture
> mainly support two kinds of prefetch mechanism in L1 data cache:
> 
> a. Data cache unit (DCU) prefetcher. Data spatial locality ask us to
> provide
>    adjacent data while handling current data. larger cache line size
>    is one choice, but it would cause more cached data to be evicted and
> latency
>    to load, so we simply prefetch next line when accessing current data.
>    This mode only prefetch data of ascending address.
> 
> b. Instruction pointer (IP)- based strided prefetcher. Based on
> Load/write
>    instruction address the mechanism predicate to prefetch data with
> adaptive stride,
>    including ascending and descending address
> 
> DCU mode is good when time program data operation spend is longer than
> that of
> prefetch next line, however copy-page function breaks the assumption,
> DCU mode is hardly helpful, specially we append software prefetch and
> data is
> in cache, so bus traffic is more busy that impact perforamnce seriously.
> 
> In this patch we introduce backward copy to successfully avoid HW
> prfetch
> impact(DCU prefetcher), and simplify original code.
> The performance on atom is improved about 11%, 8% on hot/cold-cache
> case respectively.
> (We use our micro-benchmark, and will do further test according to your
> requirement)
> 
> Thanks
> Ling
> 
> ---
> In this version we re-use prefetcht0 for atom cpu, although prefetchnta
> is better on snb.
> 
>  arch/x86/lib/copy_page_64.S |  140 +++++++++++++++++++----------------
> -------
>  1 files changed, 63 insertions(+), 77 deletions(-)
> 
> diff --git a/arch/x86/lib/copy_page_64.S b/arch/x86/lib/copy_page_64.S
> index 45f7db7..35e08fe 100644
> --- a/arch/x86/lib/copy_page_64.S
> +++ b/arch/x86/lib/copy_page_64.S
> @@ -1,4 +1,5 @@
>  /* Written 2003 by Andi Kleen, based on a kernel by Evandro Menezes */
> +/* Updated 2011 by Ma Ling to introduce backward copy */
> 
>  #include <linux/linkage.h>
>  #include <asm/dwarf2.h>
> @@ -13,89 +14,74 @@ copy_page_rep:
>  	CFI_ENDPROC
>  ENDPROC(copy_page_rep)
> 
> -/*
> -   Don't use streaming copy unless cpu indicate X86_FEATURE_REP_GOOD
> -   Could vary the prefetch distance based on SMP/UP
> -*/
> -
> +/*
> + * Don't use streaming copy unless cpu indicate X86_FEATURE_REP_GOOD.
> + * By backward copy we manage to reduce impact from HW prefetch
> + * when data is in L1 cache, and get benefit when data is not in L1
> cache.
> + */
>  ENTRY(copy_page)
>  	CFI_STARTPROC
> -	subq	$3*8, %rsp
> -	CFI_ADJUST_CFA_OFFSET 3*8
> -	movq	%rbx, (%rsp)
> -	CFI_REL_OFFSET rbx, 0
> -	movq	%r12, 1*8(%rsp)
> -	CFI_REL_OFFSET r12, 1*8
> -	movq	%r13, 2*8(%rsp)
> -	CFI_REL_OFFSET r13, 2*8
> -
> -	movl	$(4096/64)-5, %ecx
> -	.p2align 4
> +	lea	4096(%rsi), %rsi
> +	lea	4096(%rdi), %rdi
> +	mov	$(4096/64)-5, %cl
> +	mov	$5, %dl
> +	/*
> +	 * Nop force following instruction to be 16 bytes aligned.
> +	 */
> +	nop
>  .Loop64:
> -  	dec	%rcx
> -
> -	movq	0x8*0(%rsi), %rax
> -	movq	0x8*1(%rsi), %rbx
> -	movq	0x8*2(%rsi), %rdx
> -	movq	0x8*3(%rsi), %r8
> -	movq	0x8*4(%rsi), %r9
> -	movq	0x8*5(%rsi), %r10
> -	movq	0x8*6(%rsi), %r11
> -	movq	0x8*7(%rsi), %r12
> -
> -	prefetcht0 5*64(%rsi)
> -
> -	movq	%rax, 0x8*0(%rdi)
> -	movq	%rbx, 0x8*1(%rdi)
> -	movq	%rdx, 0x8*2(%rdi)
> -	movq	%r8,  0x8*3(%rdi)
> -	movq	%r9,  0x8*4(%rdi)
> -	movq	%r10, 0x8*5(%rdi)
> -	movq	%r11, 0x8*6(%rdi)
> -	movq	%r12, 0x8*7(%rdi)
> -
> -	leaq	64 (%rsi), %rsi
> -	leaq	64 (%rdi), %rdi
> -
> -	jnz	.Loop64
> -
> -	movl	$5, %ecx
> -	.p2align 4
> +	prefetcht0 -5*64(%rsi)
> +	decb	%cl
> +
> +	movq	-0x8*1(%rsi), %rax
> +	movq	-0x8*2(%rsi), %r8
> +	movq	-0x8*3(%rsi), %r9
> +	movq	-0x8*4(%rsi), %r10
> +	movq	%rax, -0x8*1(%rdi)
> +	movq	%r8, -0x8*2(%rdi)
> +	movq	%r9, -0x8*3(%rdi)
> +	movq	%r10, -0x8*4(%rdi)
> +
> +	movq	-0x8*5(%rsi), %rax
> +	movq	-0x8*6(%rsi), %r8
> +	movq	-0x8*7(%rsi), %r9
> +	movq	-0x8*8(%rsi), %r10
> +	leaq	-64(%rsi), %rsi
> +	movq	%rax, -0x8*5(%rdi)
> +	movq	%r8, -0x8*6(%rdi)
> +	movq	%r9, -0x8*7(%rdi)
> +	movq	%r10, -0x8*8(%rdi)
> +	leaq	-64(%rdi), %rdi
> +
> + 	jnz     .Loop64
> +
>  .Loop2:
> -	decl	%ecx
> -
> -	movq	0x8*0(%rsi), %rax
> -	movq	0x8*1(%rsi), %rbx
> -	movq	0x8*2(%rsi), %rdx
> -	movq	0x8*3(%rsi), %r8
> -	movq	0x8*4(%rsi), %r9
> -	movq	0x8*5(%rsi), %r10
> -	movq	0x8*6(%rsi), %r11
> -	movq	0x8*7(%rsi), %r12
> -
> -	movq	%rax, 0x8*0(%rdi)
> -	movq	%rbx, 0x8*1(%rdi)
> -	movq	%rdx, 0x8*2(%rdi)
> -	movq	%r8,  0x8*3(%rdi)
> -	movq	%r9,  0x8*4(%rdi)
> -	movq	%r10, 0x8*5(%rdi)
> -	movq	%r11, 0x8*6(%rdi)
> -	movq	%r12, 0x8*7(%rdi)
> +	decb	%dl
> +
> +	movq	-0x8*1(%rsi), %rax
> +	movq	-0x8*2(%rsi), %r8
> +	movq	-0x8*3(%rsi), %r9
> +	movq	-0x8*4(%rsi), %r10
> +	movq	%rax, -0x8*1(%rdi)
> +	movq	%r8, -0x8*2(%rdi)
> +	movq	%r9, -0x8*3(%rdi)
> +	movq	%r10, -0x8*4(%rdi)
> +
> +	movq	-0x8*5(%rsi), %rax
> +	movq	-0x8*6(%rsi), %r8
> +	movq	-0x8*7(%rsi), %r9
> +	movq	-0x8*8(%rsi), %r10
> +	leaq	-64(%rsi), %rsi
> +	movq	%rax, -0x8*5(%rdi)
> +	movq	%r8, -0x8*6(%rdi)
> +	movq	%r9, -0x8*7(%rdi)
> +	movq	%r10, -0x8*8(%rdi)
> +	leaq	-64(%rdi), %rdi
> +
> + 	jnz	.Loop2
> 
> -	leaq	64(%rdi), %rdi
> -	leaq	64(%rsi), %rsi
> -
> -	jnz	.Loop2
> -
> -	movq	(%rsp), %rbx
> -	CFI_RESTORE rbx
> -	movq	1*8(%rsp), %r12
> -	CFI_RESTORE r12
> -	movq	2*8(%rsp), %r13
> -	CFI_RESTORE r13
> -	addq	$3*8, %rsp
> -	CFI_ADJUST_CFA_OFFSET -3*8
>  	ret
> +
>  .Lcopy_page_end:
>  	CFI_ENDPROC
>  ENDPROC(copy_page)
> --
> 1.6.5.2

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