[U-Boot] [PATCH v2 2/8] arm: relocation: clear .bss section with arch memset if defined

[Przemyslaw Marczak]

Hello,

On 02/16/2015 04:13 PM, Przemyslaw Marczak wrote:
> For ARM architecture, enable the CONFIG_USE_ARCH_MEMSET/MEMCPY,
> will highly increase the memset/memcpy performance. This is able
> thanks to the ARM multiple register instructions.
>
> Unfortunatelly the relocation is done without the cache enabled,
> so it takes some time, but zeroing the BSS memory takes much more
> longer, especially for the configs with big static buffers.
>
> A quick test confirms, that the boot time improvement after using
> the arch memcpy for relocation has no significant meaning.
> The same test confirms that enable the memset for zeroing BSS,
> reduces the boot time.
>
> So this patch enables the arch memset for zeroing the BSS after
> the relocation process. For ARM boards, this can be enabled
> in board configs by defining: 'CONFIG_USE_ARCH_MEMSET'.
>
> This was tested on Trats2.
> A quick test with trace. Boot time from start to main_loop() entry:
> - ~1384ms - before this change
> -  ~888ms - after this change
>
> Signed-off-by: Przemyslaw Marczak <p.marczak at samsung.com>
> Cc: Albert Aribaud <albert.u.boot at aribaud.net>
> Cc: Tom Rini <trini at ti.com>
> ---
>   arch/arm/lib/crt0.S | 10 +++++++++-
>   1 file changed, 9 insertions(+), 1 deletion(-)
>
> diff --git a/arch/arm/lib/crt0.S b/arch/arm/lib/crt0.S
> index 22df3e5..fab3d2c 100644
> --- a/arch/arm/lib/crt0.S
> +++ b/arch/arm/lib/crt0.S
> @@ -115,14 +115,22 @@ here:
>   	bl	c_runtime_cpu_setup	/* we still call old routine here */
>
>   	ldr	r0, =__bss_start	/* this is auto-relocated! */
> -	ldr	r1, =__bss_end		/* this is auto-relocated! */
>
> +#ifdef CONFIG_USE_ARCH_MEMSET
> +	ldr	r3, =__bss_end		/* this is auto-relocated! */
> +	mov	r1, #0x00000000		/* prepare zero to clear BSS */
> +
> +	subs	r2, r3, r0		/* r2 = memset len */
> +	bl	memset
> +#else
> +	ldr	r1, =__bss_end		/* this is auto-relocated! */
>   	mov	r2, #0x00000000		/* prepare zero to clear BSS */
>
>   clbss_l:cmp	r0, r1			/* while not at end of BSS */
>   	strlo	r2, [r0]		/* clear 32-bit BSS word */
>   	addlo	r0, r0, #4		/* move to next */
>   	blo	clbss_l
> +#endif
>
>   	bl coloured_LED_init
>   	bl red_led_on
>

This commit left unchanged. After boot time test using oscilloscope and 
the clock cycle counter I didn't noticed a time difference in more then 
one ms. In this case I think that insert a duplicated code here, has no 
sense.

Best regards,
-- 
Przemyslaw Marczak
Samsung R&D Institute Poland
Samsung Electronics
p.marczak at samsung.com