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From: Szabolcs Nagy via Libc-alpha <libc-alpha@sourceware.org>
To: Wilco Dijkstra <Wilco.Dijkstra@arm.com>
Cc: 'GNU C Library' <libc-alpha@sourceware.org>
Subject: Re: [PATCH v4 2/5] AArch64: Improve A64FX memset for large sizes
Date: Tue, 10 Aug 2021 10:38:31 +0100
Message-ID: <20210810093830.GD20410@arm.com>

The 08/09/2021 16:17, Wilco Dijkstra via Libc-alpha wrote:
> v4: Slightly tweak alignment code
> 
> Improve performance of large memsets. Simplify alignment code. For zero memset use DC ZVA,
> which almost doubles performance. For non-zero memsets use the unroll8 loop which is about 10% faster.


this is OK to commit.

you should keep

Reviewed-by: Naohiro Tamura <naohirot@fujitsu.com>

in the commit message if there are only minor tweaks or no changes.

> 
> ---
> 
> diff --git a/sysdeps/aarch64/multiarch/memset_a64fx.S b/sysdeps/aarch64/multiarch/memset_a64fx.S
> index cf3d402ef681a9d98964d1751537945692a1ae68..6bc8ef5e0c84dbb59a57d114ae6ec8e3fa3822ad 100644
> --- a/sysdeps/aarch64/multiarch/memset_a64fx.S
> +++ b/sysdeps/aarch64/multiarch/memset_a64fx.S
> @@ -27,14 +27,11 @@
>   */
>  
>  #define L1_SIZE		(64*1024)	// L1 64KB
> -#define L2_SIZE         (8*1024*1024)	// L2 8MB - 1MB
> +#define L2_SIZE         (8*1024*1024)	// L2 8MB
>  #define CACHE_LINE_SIZE	256
>  #define PF_DIST_L1	(CACHE_LINE_SIZE * 16)	// Prefetch distance L1
> -#define ZF_DIST		(CACHE_LINE_SIZE * 21)	// Zerofill distance
> -#define rest		x8
> +#define rest		x2
>  #define vector_length	x9
> -#define vl_remainder	x10	// vector_length remainder
> -#define cl_remainder	x11	// CACHE_LINE_SIZE remainder
>  
>  #if HAVE_AARCH64_SVE_ASM
>  # if IS_IN (libc)
> @@ -42,14 +39,6 @@
>  
>  	.arch armv8.2-a+sve
>  
> -	.macro dc_zva times
> -	dc	zva, tmp1
> -	add	tmp1, tmp1, CACHE_LINE_SIZE
> -	.if \times-1
> -	dc_zva "(\times-1)"
> -	.endif
> -	.endm
> -
>  	.macro st1b_unroll first=0, last=7
>  	st1b	z0.b, p0, [dst, \first, mul vl]
>  	.if \last-\first
> @@ -188,54 +177,30 @@ L(L1_prefetch): // if rest >= L1_SIZE
>  	cbnz	rest, L(unroll32)
>  	ret
>  
> -L(L2):
> -	// align dst address at vector_length byte boundary
> -	sub	tmp1, vector_length, 1
> -	ands	tmp2, dst, tmp1
> -	// if vl_remainder == 0
> -	b.eq	1f
> -	sub	vl_remainder, vector_length, tmp2
> -	// process remainder until the first vector_length boundary
> -	whilelt	p2.b, xzr, vl_remainder
> -	st1b	z0.b, p2, [dst]
> -	add	dst, dst, vl_remainder
> -	sub	rest, rest, vl_remainder
> -	// align dstin address at CACHE_LINE_SIZE byte boundary
> -1:	mov	tmp1, CACHE_LINE_SIZE
> -	ands	tmp2, dst, CACHE_LINE_SIZE - 1
> -	// if cl_remainder == 0
> -	b.eq	L(L2_dc_zva)
> -	sub	cl_remainder, tmp1, tmp2
> -	// process remainder until the first CACHE_LINE_SIZE boundary
> -	mov	tmp1, xzr       // index
> -2:	whilelt	p2.b, tmp1, cl_remainder
> -	st1b	z0.b, p2, [dst, tmp1]
> -	incb	tmp1
> -	cmp	tmp1, cl_remainder
> -	b.lo	2b
> -	add	dst, dst, cl_remainder
> -	sub	rest, rest, cl_remainder
> -
> -L(L2_dc_zva):
> -	// zero fill
> -	mov	tmp1, dst
> -	dc_zva	(ZF_DIST / CACHE_LINE_SIZE) - 1
> -	mov	zva_len, ZF_DIST
> -	add	tmp1, zva_len, CACHE_LINE_SIZE * 2
> -	// unroll
> +	// count >= L2_SIZE
>  	.p2align 3
> -1:	st1b_unroll 0, 3
> -	add	tmp2, dst, zva_len
> -	dc	 zva, tmp2
> -	st1b_unroll 4, 7
> -	add	tmp2, tmp2, CACHE_LINE_SIZE
> -	dc	zva, tmp2
> -	add	dst, dst, CACHE_LINE_SIZE * 2
> -	sub	rest, rest, CACHE_LINE_SIZE * 2
> -	cmp	rest, tmp1	// ZF_DIST + CACHE_LINE_SIZE * 2
> -	b.ge	1b
> -	cbnz	rest, L(unroll8)
> -	ret
> +L(L2):
> +	tst	valw, 255
> +	b.ne	L(unroll8)
> +	// align dst to CACHE_LINE_SIZE byte boundary
> +	and	tmp2, dst, CACHE_LINE_SIZE - 1
> +	st1b	z0.b, p0, [dst, 0, mul vl]
> +	st1b	z0.b, p0, [dst, 1, mul vl]
> +	st1b	z0.b, p0, [dst, 2, mul vl]
> +	st1b	z0.b, p0, [dst, 3, mul vl]
> +	sub	dst, dst, tmp2
> +	add	count, count, tmp2
> +
> +	// clear cachelines using DC ZVA
> +	sub	count, count, CACHE_LINE_SIZE * 2
> +	.p2align 4
> +1:	add	dst, dst, CACHE_LINE_SIZE
> +	dc	zva, dst
> +	subs	count, count, CACHE_LINE_SIZE
> +	b.hi	1b
> +	add	count, count, CACHE_LINE_SIZE
> +	add	dst, dst, CACHE_LINE_SIZE
> +	b	L(last)
>  
>  END (MEMSET)
>  libc_hidden_builtin_def (MEMSET)
> 

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