[Skiboot] [RFC PATCH] Use two VSX registers to do initial copy of skiboot

[Benjamin Herrenschmidt]

On Thu, 2015-05-21 at 18:40 +1000, Stewart Smith wrote:
> Note my awful fiddling of MSR so that I can use VSX registers :)

Is this really worth it ? :-) I like being conservative in that code...

> In the hello_world test running in mambo, we get the following reduction
> in instruction/cycle count:
> Before:
> 20284943: ** finished running 20284942 instructions **
> 
> Single VSX register:
> 19687022: ** finished running 19641315 instructions **
> 
> using 2 vsx registers:
> 19621488: ** finished running 19575781 instructions **
> 19621488: ** finished running 19575781 instructions **
> 
> 65534 fewer cycles & instructions than just 1
> 709161 fewer than base implementation
> 
> using 3 vsx regs:
> 19883634: ** finished running 19837927 instructions **
> 
> Signed-off-by: Stewart Smith <stewart at linux.vnet.ibm.com>
> ---
>  asm/head.S |   24 +++++++++++++++++++-----
>  1 file changed, 19 insertions(+), 5 deletions(-)
> 
> diff --git a/asm/head.S b/asm/head.S
> index fd6e3fb..9b3d7bb 100644
> --- a/asm/head.S
> +++ b/asm/head.S
> @@ -314,16 +314,30 @@ boot_entry:
>  	cmpd	%r29,%r30
>  	beq	2f
>  	LOAD_IMM32(%r3, _sbss - __head)
> -	srdi	%r3,%r3,3
> +	srdi	%r3,%r3,5
>  	mtctr	%r3
> +	mfmsr	%r24
> +	mfmsr	%r4
> +	oris	%r4,%r4, (1<<13)@h
> +	oris	%r4,%r4, (1<<23)@h
> +	oris	%r4,%r4, (1<<25)@h
> +	mtmsr	%r4
>  	mr	%r4,%r30
>  	mr	%r15,%r30
>  	mr	%r30,%r29
> -1:	ld	%r0,0(%r4)
> -	std	%r0,0(%r29)
> -	addi	%r29,%r29,8
> -	addi	%r4,%r4,8
> +	addi	%r5,%r4,16
> +	addi	%r6,%r29,16
> +	
> +1:	lxvd2x	%vs1,%r0,%r4
> +	lxvd2x	%vs2,%r0,%r5
> +	stxvd2x	%vs1,%r0,%r29
> +	stxvd2x	%vs2,%r0,%r6
> +	addi	%r29,%r29,16
> +	addi	%r4,%r4,16
> +	addi    %r5,%r5,16
> +        addi    %r6,%r6,16
>  	bdnz	1b
> +	mtmsr	%r24
>  	sync
>  	icbi	0,%r29
>  	sync