[U-Boot] fdt performance

[Aaron Williams]

Hi Simon,

Sorry for the long delay.


On 10/17/2013 03:27 PM, Simon Glass wrote:
> Hi Aaron,
>
> On Thu, Oct 17, 2013 at 12:24 AM, Aaron Williams
> <Aaron.Williams at caviumnetworks.com> wrote:
>> Hi all,
>>
>> In our bootloader based off of 2013.07 we make extensive use of the flat
>> device tree. In profiling our bootloader in our simulator I found that the
>> function eating up the most time is fdt_next_tag. Looking at it, especially
>> fdt_offset_ptr, it looks like there is a lot of room for improvement
>> especially in the skip name section.
>>
>> Some of the checks in fdt_offset_ptr also look useless, such as if ((offset
>> + len) < offset) which will always be false, or
>> if (p + len < p)
>>
>> len is always positive.
> Are you using CONFIG_OF_CONTROL?
>
> If so, as a higher-level point, we could bring in an efficient DT
> library, which converts the the FDT into a tree structure for faster
> parsing. I can point you to a starting point if you like.
>
> Regards,
> Simon
A higher-level point is not desirable since when we are experiencing the 
performance issues we are running out of NOR flash or our simulator. 
Since most of our customers use NOR flash this a huge issue for us. We 
have very little memory available for holding data structures since 
basically only the stack is available before relocation.

Taking out these checks significantly sped up our boot process.

If you're checking for a wrap-around it should not check for each byte 
but should check only once if it will wrap and handle it accordingly. If 
we're wrapping then the device tree is hosed and we have bigger problems.

-Aaron

-- 
Aaron Williams
Software Engineer
Cavium, Inc.
(408) 943-7198  (510) 789-8988 (cell)