[PATCH RFC] Imporve 64bit memset performance for Haswell CPU with AVX2 instruction

[Ling Ma]

I will send the next version after performance test according to your comments.

Thanks
Ling

2014-06-06 0:32 GMT+08:00, Ondřej Bílka <neleai@seznam.cz>:
> On Wed, Jun 04, 2014 at 03:00:05PM +0800, Ling Ma wrote:
>> H.J
>>
>> The website changed IP, now the code is available again:
>>  http://www.yunos.org/tmp/memset-avx2.patch ,
>> and also gziped as attachment in this mail.
>>
>> Thanks
>> Ling
>>
>
> Now performance looks ok for me, but few formating problems.
> With these fixed I would be satisfied H.J do you have comments?
>
> There is possible followup to also optimize __bzero like we do in
> general case.
>
> Then second followup would be decrease function size by reshuffling
> blocks, on several places there are 15/16 free bytes due alignment.
>
> Formatting problems are here:
>
> +	vpxor	%xmm0, %xmm0, %xmm0
> +	vmovd %esi, %xmm1
> +	mov	%rdi, %rsi
> +	mov	%rdi, %rax
>
> here
>
> +L(less_16bytes):
> +	vmovd %xmm0, %rcx
> +	cmp	$8, %dl
> +	jb	L(less_8bytes)
> +	mov %rcx, (%rdi)
> +	mov %rcx, -0x08(%rsi)
> +	ret
> +
> +	.p2align 4
> +L(less_8bytes):
> +	cmp	$4, %dl
> +	jb	L(less_4bytes)
> +	mov %ecx, (%rdi)
> +	mov %ecx, -0x04(%rsi)
> +	ret
>
> and here
>
> +	mov	%rax, %rsi
> +	vmovd %xmm0, %eax
> +	mov	%rdx, %rcx
>
> As I mentioned code size one trick is that instructions
> with -128 argument are shorter than with 128. You could save 16
> bytes with following modification, however it must be tested if
> it improves performance.
>
>
> --- x	2014-06-05 18:20:35.313645591 +0200
> +++ sysdeps/x86_64/multiarch/memset-avx2.S	2014-06-05
> 18:22:25.068642767 +0200
> @@ -95,7 +95,6 @@
>  	.p2align 4
>  L(256bytesormore):
>  	vinserti128 $1, %xmm0, %ymm0, %ymm0
> -	mov	$0x80, %rcx
>  	add	%rdx, %rsi
>  	mov	%rdi, %r9
>  	vmovdqu	%ymm0, (%rdi)
> @@ -105,15 +104,15 @@
>  	add	%r9, %rdx
>  	cmp	$4096, %rdx
>  	ja	L(gobble_data)
> -	sub	%ecx, %edx
> +	add	$-128, %edx
>  L(gobble_128_loop):
>  	vmovdqa	%ymm0, (%rdi)
>  	vmovdqa	%ymm0, 0x20(%rdi)
>  	vmovdqa	%ymm0, 0x40(%rdi)
>  	vmovdqa	%ymm0, 0x60(%rdi)
> -	add	%rcx, %rdi
> -	sub	%ecx, %edx
> -	jae	L(gobble_128_loop)
> +	sub	$-128, %rdi
> +	add	$-128, %edx
> +	jb	L(gobble_128_loop)
>  	vmovdqu	%ymm0, -0x80(%rsi)
>  	vmovdqu	%ymm0, -0x60(%rsi)
>  	vmovdqu	%ymm0, -0x40(%rsi)
>
>