[U-Boot] [PATCH 0/3] arm: reduce .bss section clear time

[Przemyslaw Marczak]

Hello,

On 01/28/2015 03:34 PM, Pantelis Antoniou wrote:
> Hi Przemyslaw,
>
>> On Jan 28, 2015, at 16:30 , Przemyslaw Marczak <p.marczak at samsung.com> wrote:
>>
>> Hello,
>>
>> On 01/28/2015 03:18 PM, Pantelis Antoniou wrote:
>>> Hi Przemyslaw,
>>>
>>>> On Jan 28, 2015, at 16:10 , Przemyslaw Marczak <p.marczak at samsung.com> wrote:
>>>>
>>>> Hello Stefan,
>>>>
>>>> On 01/28/2015 02:12 PM, Stefan Roese wrote:
>>>>> Hi Przemyslaw,
>>>>>
>>>>> On 28.01.2015 13:55, Przemyslaw Marczak wrote:
>>>>>> This patchset reduces the boot time for ARM architecture,
>>>>>> Exynos boards, and boards with DFU enabled(ARM).
>>>>>>
>>>>>> For tested Trats2 device, this was done in three steps.
>>>>>>
>>>>>> First was enable the arch memcpy and memset.
>>>>>> The second step was enable memset for .bss clear.
>>>>>> The third step for reduce this operation is to keep .bss section
>>>>>> small as possible.
>>>>>>
>>>>>> The .bss section will grow if we have a lot of static variables.
>>>>>> This section is cleared before jump to the relocated U-Boot,
>>>>>> and it's done word by word. To reduce the time for this step,
>>>>>> we can enable arch memset, which uses multiple ARM registers.
>>>>>>
>>>>>> For configs with DFU enabled, we can find the dfu buffer in this section,
>>>>>> which has at least 8MB (32MB for trats2). This is a lot of useless data,
>>>>>> which is not required for standard boot. So this buffer should be dynamic
>>>>>> allocated.
>>>>>>
>>>>>> Przemyslaw Marczak (3):
>>>>>>    exynos: config: enable arch memcpy and arch memset
>>>>>>    arm: relocation: clear .bss section with arch memset if defined
>>>>>>    dfu: mmc: file buffer: remove static allocation
>>>>>>
>>>>>>   arch/arm/lib/crt0.S             | 10 +++++++++-
>>>>>>   drivers/dfu/dfu_mmc.c           | 25 ++++++++++++++++++++++---
>>>>>>   include/configs/exynos-common.h |  3 +++
>>>>>>   3 files changed, 34 insertions(+), 4 deletions(-)
>>>>>
>>>>> Looking at the commit messages of this patchset I can conclude that your
>>>>> overall boot time reduction is:
>>>>>
>>>>> from ~1527ms
>>>>> to ~464ms
>>>>>
>>>>> This is amazing! Congrats. :)
>>>>>
>>>>
>>>> Thank you. I was also amazed.
>>>>
>>>> The time results are taken with from the clock cycle counter, I think it's reliable. Some day I would like to check it using the oscilloscope.
>>>>
>>>>> We really should in general make more use of the optimized functions and
>>>>> take care that the buffers (e.g. the DFU buffer in this case) are used
>>>>> in a sane way.
>>>>>
>>>>> Thanks,
>>>>> Stefan
>>>>>
>>>>>
>>>>
>>>> Yes you're right, I thought that Exynos config has enabled arch memcpy/set lib, before I checked this…
>>>>
>>>
>>> Those numbers are indeed incredible; I suppose the caches are disabled?
>>>
>>>
>>
>> The caches are enabled after the relocation, in one of board_init_r calls.
>>
>
> How big is this .bss section? We’re talking about something that takes 1.5secs to clear
> a few MBs of memory? This is horrible.
>
> Even at the optimized case .5secs is too much.
>

The .bss section was about 32.3 MB, where the 32MB were required for dfu 
file buf. With the third patch, the .bss section is about 300k.
I'm not saying, that this is fast booting. But the achieved improvement 
is really good for this config

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

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