linux-kernel - Re: [PATCH 2/4] Accelerated CRC T10 DIF computation with PCLMULQDQ instruction

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Date:	Wed, 17 Apr 2013 20:58:30 +0300
From:	Jussi Kivilinna <jussi.kivilinna@....fi>
To:	Tim Chen <tim.c.chen@...ux.intel.com>
CC:	Herbert Xu <herbert@...dor.apana.org.au>,
	"H. Peter Anvin" <hpa@...or.com>,
	"David S. Miller" <davem@...emloft.net>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	James Bottomley <James.Bottomley@...senPartnership.com>,
	Matthew Wilcox <willy@...ux.intel.com>,
	Jim Kukunas <james.t.kukunas@...ux.intel.com>,
	Keith Busch <keith.busch@...el.com>,
	Erdinc Ozturk <erdinc.ozturk@...el.com>,
	Vinodh Gopal <vinodh.gopal@...el.com>,
	James Guilford <james.guilford@...el.com>,
	Wajdi Feghali <wajdi.k.feghali@...el.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-crypto@...r.kernel.org, linux-scsi@...r.kernel.org
Subject: Re: [PATCH 2/4] Accelerated CRC T10 DIF computation with PCLMULQDQ
 instruction

On 16.04.2013 19:20, Tim Chen wrote:
> This is the x86_64 CRC T10 DIF transform accelerated with the PCLMULQDQ
> instructions.  Details discussing the implementation can be found in the
> paper:
> 
> "Fast CRC Computation for Generic Polynomials Using PCLMULQDQ Instruction"
> URL: http://download.intel.com/design/intarch/papers/323102.pdf

URL does not work.

> 
> Signed-off-by: Tim Chen <tim.c.chen@...ux.intel.com>
> Tested-by: Keith Busch <keith.busch@...el.com>
> ---
>  arch/x86/crypto/crct10dif-pcl-asm_64.S | 659 +++++++++++++++++++++++++++++++++
>  1 file changed, 659 insertions(+)
>  create mode 100644 arch/x86/crypto/crct10dif-pcl-asm_64.S
<snip>
> +
> +	# Allocate Stack Space
> +	mov     %rsp, %rcx
> +	sub	$16*10, %rsp
> +	and     $~(0x20 - 1), %rsp
> +
> +	# push the xmm registers into the stack to maintain
> +	movdqa %xmm10, 16*2(%rsp)
> +	movdqa %xmm11, 16*3(%rsp)
> +	movdqa %xmm8 , 16*4(%rsp)
> +	movdqa %xmm12, 16*5(%rsp)
> +	movdqa %xmm13, 16*6(%rsp)
> +	movdqa %xmm6,  16*7(%rsp)
> +	movdqa %xmm7,  16*8(%rsp)
> +	movdqa %xmm9,  16*9(%rsp)

You don't need to store (and restore) these, as 'crc_t10dif_pcl' is called between kernel_fpu_begin/_end.

> +
> +
> +	# check if smaller than 256
> +	cmp	$256, arg3
> +
<snip>
> +_cleanup:
> +	# scale the result back to 16 bits
> +	shr	$16, %eax
> +	movdqa	16*2(%rsp), %xmm10
> +	movdqa	16*3(%rsp), %xmm11
> +	movdqa	16*4(%rsp), %xmm8
> +	movdqa	16*5(%rsp), %xmm12
> +	movdqa	16*6(%rsp), %xmm13
> +	movdqa	16*7(%rsp), %xmm6
> +	movdqa	16*8(%rsp), %xmm7
> +	movdqa	16*9(%rsp), %xmm9

Registers are overwritten by kernel_fpu_end.

> +	mov     %rcx, %rsp
> +	ret
> +ENDPROC(crc_t10dif_pcl)
> +

You should move ENDPROC at end of the full function.

> +########################################################################
> +
> +.align 16
> +_less_than_128:
> +
> +	# check if there is enough buffer to be able to fold 16B at a time
> +	cmp	$32, arg3
<snip>
> +	movdqa	(%rsp), %xmm7
> +	pshufb	%xmm11, %xmm7
> +	pxor	%xmm0 , %xmm7   # xor the initial crc value
> +
> +	psrldq	$7, %xmm7
> +
> +	jmp	_barrett

Move ENDPROC here.


 -Jussi
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