linux-kernel - Re: [PATCH] [s390]: Use .rept directive to store/load fpu registers

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Message-ID: <55E55904.1070606@de.ibm.com>
Date:	Tue, 01 Sep 2015 09:51:32 +0200
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Alexander Kuleshov <kuleshovmail@...il.com>,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>
CC:	linux390@...ibm.com, linux-s390@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] [s390]: Use .rept directive to store/load fpu registers

Am 28.08.2015 um 15:49 schrieb Alexander Kuleshov:
> We can use .rept directive to simplify/decrease assembly code
> that makes storing and loading floating point registers in the
> arch/s390/kernel/swsusp.S.
> 
> The resulting code after the patch is the same that before
> 
>  2c4:	68 00 d2 00       	ld	%f0,512(%r13)
>  2c8:	68 10 d2 08       	ld	%f1,520(%r13)
>  2cc:	68 20 d2 10       	ld	%f2,528(%r13)
>  2d0:	68 30 d2 18       	ld	%f3,536(%r13)
>  2d4:	68 40 d2 20       	ld	%f4,544(%r13)
>  2d8:	68 50 d2 28       	ld	%f5,552(%r13)
>  2dc:	68 60 d2 30       	ld	%f6,560(%r13)
>  2e0:	68 70 d2 38       	ld	%f7,568(%r13)
>  2e4:	68 80 d2 40       	ld	%f8,576(%r13)
>  2e8:	68 90 d2 48       	ld	%f9,584(%r13)
>  2ec:	68 a0 d2 50       	ld	%f10,592(%r13)
>  2f0:	68 b0 d2 58       	ld	%f11,600(%r13)
>  2f4:	68 c0 d2 60       	ld	%f12,608(%r13)
>  2f8:	68 d0 d2 68       	ld	%f13,616(%r13)
>  2fc:	68 e0 d2 70       	ld	%f14,624(%r13)
>  300:	68 f0 d2 78       	ld	%f15,632(%r13)
> 
> Signed-off-by: Alexander Kuleshov <kuleshovmail@...il.com>
> ---
>  arch/s390/kernel/swsusp.S | 49 ++++++++++++++++-------------------------------
>  1 file changed, 17 insertions(+), 32 deletions(-)
> 
> diff --git a/arch/s390/kernel/swsusp.S b/arch/s390/kernel/swsusp.S
> index ca62946..8011e14 100644
> --- a/arch/s390/kernel/swsusp.S
> +++ b/arch/s390/kernel/swsusp.S
> @@ -48,22 +48,15 @@ ENTRY(swsusp_arch_suspend)
>  	/* Store registers */
>  	mvc	0x318(4,%r1),__SF_EMPTY(%r15)	/* move prefix to lowcore */
>  	stfpc	0x31c(%r1)			/* store fpu control */
> -	std	0,0x200(%r1)			/* store f0 */
> -	std	1,0x208(%r1)			/* store f1 */
> -	std	2,0x210(%r1)			/* store f2 */
> -	std	3,0x218(%r1)			/* store f3 */
> -	std	4,0x220(%r1)			/* store f4 */
> -	std	5,0x228(%r1)			/* store f5 */
> -	std	6,0x230(%r1)			/* store f6 */
> -	std	7,0x238(%r1)			/* store f7 */
> -	std	8,0x240(%r1)			/* store f8 */
> -	std	9,0x248(%r1)			/* store f9 */
> -	std	10,0x250(%r1)			/* store f10 */
> -	std	11,0x258(%r1)			/* store f11 */
> -	std	12,0x260(%r1)			/* store f12 */
> -	std	13,0x268(%r1)			/* store f13 */
> -	std	14,0x270(%r1)			/* store f14 */
> -	std	15,0x278(%r1)			/* store f15 */
> +
> +	/* store f0..f15 floating point registers */
> +	.set i, 0
> +	.set f, 0x200
> +	.rept 16
> +	std i, f(%r1)
> +	.set i, (i+1)
> +	.set f, (f+0x8)
> +	.endr

I personally find the existing code easier to read, especially as it matches the
assembler output and I can directly where the slots are, (e.g. f11 is 0x258)

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