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

[Simon Glass]

Hi Przemyslaw,

On 16 February 2015 at 08:21, Przemyslaw Marczak <p.marczak at samsung.com> wrote:
> 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.

I don't understand this comment, sorry.

Regards,
Simon