Hi Jammy & Mingliang,
On 2/5/21 2:59 AM, Jammy Zhou wrote:
Hi,
There are several ideas for DT improvements. Please check if they are
reasonable, and any comments are welcome. I would let Mingliang (CCed)
share more details if needed.
1) Improve search algorithm performance: Is the binary search tree or other
algorithm better than current algorithm?
We will need data to show the problem. I suppose this would best be
done when unflatening the data at runtime? What is the expected gain in
boot time? Are there any measurements of how much time is spent in the
search routines today?
2) Reduce DTB space: when use one DTB to support multiple boards, the image
is quite big (e.g, ~39MB space for 100 configurations), and some
compression algorithm can reduce the space a lot (e.g, from 39MB to 7MB).
Shall we have such compression support for DTB? And it can be helpful if we
can have more efficient compression algorithm.
This could be done as an enhancement to the DTB loader instead of the
DTB format itself.
Compressing each DTB (boardx.dtb.xz) will get you gains but compressing
a set of boards (vmlinux-5.4.0-65-generic-dbt-set-20.tar.xz) might give
you more.
To be significant, the number of boards would need to be large and the
size of the rootfs would need to be modest. A 200 to 300 MB minimal
image would make an interesting comparison point. (A rootfs of 10s of
MB would probably only target a few boards.)
What is the goal of the use case?
1) Fit in limited storage ( ex: 256MB )
2) Conserve more space of modest storage for container data ( 1GB eMMC)
3) Improve boot time
For 3, the load time will be reduced but the decompression time will be
added. These need to be balanced based on the CPU.
One pet peeve I have in most of our boot loaders today is that they do
loading and decompression serially. During loading the IO is 100%
loaded and the CPU is very lightly loaded. During decomoression the CPU
is 100% loaded and the IO is 0%. It makes sense to pipleline / overlap
these things which means that it needs to go into the loader. To
optimize boot time the decompression algorithm needs to be chosen
correctly. On smaller CPUs the time taken to decompress newer
algorithms can greatly outweigh the time taken to load the decompressed
data. Ideally the time to decompress 1 block == time to load one block.
The dynamics shift with CPU and IO performance.
Today, a lot of people focused on boot speed just use decompressed data
but I think we could do better if we pipeline
3) Define specific rule for properties: The property value (FDT_PROP_DATA)
itself occupies only ~50% of the total DTB space. And the property of each
node is different and the private property name length is too long, for
example: “freq-autodown-baseaddress-num” in dt_strings. It seems more
reasonable that the property value should occupies more than 70% of the
total DTB space. It can probably be achieved to define some rules to
restrict the length of property name, etc.
This is harder. In 2019 I had proposed an ATOM based DTB enhancement
[2]. I was told Frank Rowand had other proposals for format changes.
Thanks,
Bill
[2]
https://docs.google.com/document/d/19XbxN-zX-GYwOXdF78lGnp0j7UNx1MT3wzyCjaitO9E/edit?usp=sharing
Thanks,
Jammy
_______________________________________________
boot-architecture mailing list
[email protected]
https://lists.linaro.org/mailman/listinfo/boot-architecture
--
Bill Mills
Principal Technical Consultant, Linaro
+1-240-643-0836
TZ: US Eastern
Work Schedule: Tues/Wed/Thur
_______________________________________________
boot-architecture mailing list
[email protected]
https://lists.linaro.org/mailman/listinfo/boot-architecture
