Jerry Van Baren wrote:
Wolfgang Grandegger wrote:
Hi Jerry,
Wolfgang Grandegger wrote:
Jerry Van Baren wrote:
[snip]
Yes, blob parsing will be done from the start of the blob until an answer is found every time a question is asked of it. Not a paradigm of efficiency. :-/
WRT the cached version, I have doubts about how much time it will save since I expect the "find compatible" will only be used during initialization. Is it worth optimizing? Really slow memory - yes. Fast memory - I doubt it. a) I don't picture blobs being stored in really slow memory (no i2c memories). b) If the memory really is slow, it seems like it would be as good or better to copy the blob to RAM and use it out of RAM (but there may be chicken & egg problems with that - I don't know how deeply you are looking to embed this).
I don't know what board/processor/memory you are ultimately targeting with this, so my criticisms may not be valid. I know denx.de support(s|ed) some very slow to boot boards that lots of tricks were done WRT optimization of env variables because they were stored in i2c memory.
I'm doing that for a MPC823 at 50 MHz, a very low-end system, and almost to slow for 2.6. I will do some real measurements when time permits to get a better feeling.
Here are the results of some quick measurements on my MPC855 at 80/40 MHz with the attached code example and my DTS test file:
from FLASH from MemoryNon-cached: 11116 us 1703 us Cached : 2800 us 6226 us
Well, I think we can drop the cached version even if its 4 times faster, as it make life more difficult, especially in case the FDT gets updated.
Wolfgang.
Risk & reward. The reward is pretty substantial if you read directly from slow flash, but iffy for faster RAM.
In the "from Memory" column, do you have the numbers switched? The non-cached is shown as being 4x faster than the cached.
Yes, a cut & paste error, sorry.
To be a fair comparison, the "from Memory" column also needs the time it would take to copy the blob from flash to RAM added, yes? That penalty can be bypassed by loading the blob directly into RAM via tftp or the copy to RAM time may already be part of the boot process, but it should be identified.
Here is the revised list:
from FLASH from Memory Non-cached: 11116 us 6226 us Cached : 2800 us 1703 us (2096 us)
The number in brackets is _with_ memcpy. The FDT should normally be access from memory, I fully agree.
Wolfgang.