Re: [PATCH v2] ARM: Improve armv7 memcpy performance.

["Carlos O'Donell" <carlos@redhat.com>]

On 08/30/2013 11:09 AM, Will Newton wrote:
> 
> Only enter the aligned copy loop with buffers that can be 8-byte
> aligned. This improves performance slightly on Cortex-A9 and
> Cortex-A15 cores for large copies with buffers that are 4-byte
> aligned but not 8-byte aligned.
> 
> ports/ChangeLog.arm:
> 
> 2013-08-30  Will Newton  <will.newton@linaro.org>
> 
> 	* sysdeps/arm/armv7/multiarch/memcpy_impl.S: Tighten check
> 	on entry to aligned copy loop to improve performance.

How did you test this?

Did you use the glibc performance microbenchmark?

Does the microbenchmark show gains with this change? What are the numbers?

Cheers,
Carlos.

> ---
>  ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S | 4 ++--
>  1 file changed, 2 insertions(+), 2 deletions(-)
> 
> Changes in v2:
>  - Improved description
> 
> diff --git a/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S b/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S
> index 3decad6..6e84173 100644
> --- a/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S
> +++ b/ports/sysdeps/arm/armv7/multiarch/memcpy_impl.S
> @@ -369,8 +369,8 @@ ENTRY(memcpy)
>  	cfi_adjust_cfa_offset (FRAME_SIZE)
>  	cfi_rel_offset (tmp2, 0)
>  	cfi_remember_state
> -	and	tmp2, src, #3
> -	and	tmp1, dst, #3
> +	and	tmp2, src, #7
> +	and	tmp1, dst, #7
>  	cmp	tmp1, tmp2
>  	bne	.Lcpy_notaligned
>