5 sec boot

[Mitch Bradley]

Memory to memory copy: 500 MB/s
Raw NAND FLASH read:    20 MB/s
Security hash:           4 MB/s

So overlapping hash calculation with NAND FLASH read is of limited 
value, and trying to overlap anything with memory copy is almost 
certainly counterproductive.

This discussion seem to be degenerating into a brainstorming session 
about an sub-problem that is pretty well under control (the firmware 
component of the boot time).  I've been working diligently on that 
sub-problem for nearly 2 years now, and I think I have an excellent 
grasp of where the cycles are going and what can be done to improve it.  
The only significant opportunity at this point is to reduce the JFFS2 
time, which will require either partitioning or abandoning JFFS2 for the 
boot files, or both.  UBI+UBIFS is one workable approach in the context 
of a Linux-only machine.  There are some others, such as Redboot 
partitions with a small boot partition and a large system partition, 
with various FS possibilities for the two partitions.  The quickest path 
to a deliverable system would be Redboot + JFFS2 boot partition + UBI 
system partition.

The rest of the "fruit" on the tree is solidly in the OS domain, 
encompassing kernel startup, userland startup/initscripts, X startup, 
and Sugar / application startup.  I would encourage each of you to 
address the areas in which you have special expertise, and then to take 
action.