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

[Pantelis Antoniou]

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?


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

Regards

— Pantelis