[Arm-netbook] uh-oh....

[Gordan Bobic]

On 12/29/2011 09:15 PM, lkcl luke wrote:
> On Thu, Dec 29, 2011 at 8:20 PM, Gordan Bobic<gordan at bobich.net>  wrote:
>
>> Does anyone know if a NEON equipped ARM can handle real-time video
>> decoding at a sufficient speed?
>
>   it's something like... 720mhz single-core can just about handle....
> 720p.  i think.  you need 4x that to do 1080p30, and 8x to do 1080p60
> (which is the full HD standard).
>
>   the problem is not so much the NEON itself, it's that the amount of
> data involved, just in 1920x1080 at 30fps, is 190mbytes per second.  if
> you want to do the full HD standard that's double - 380mbytes per
> second.
>
>   in other words, it doesn't matter for ARM CPUs that haven't taken
> this into account, even if you have 800mhz DDR2 RAM: the data transfer
> rates will be bitch-smacking the caches and saturating the internal
> buses.
>
>   bottom line, you really do need an ARM CPU that has an internal
> architecture which takes into account these massive data transfer
> rates.  which is why i really like the allwinner a10, because it's
> designed to cope with _four_ times more data than 1080p30.

Sure, but I'm talking about a tradeof between performance and openness. 
Very few people have HD videos. Most people are more than happy to make 
do with DVD quality, and 10in devices are typically at most 720p, 
usually 1024x600.

So arguably, what can be done in software is fine for the vast majority 
of users.

The point I'm getting at is - what happens when the manufacturer decided 
they cannot be bothered to support a particular Xorg ABI any more, or 
they cannot be bothered to update the driver to work with the new Xorg? 
At that point we are basically screwed and have no upgrade path and no 
supportability. The best we can hope to do is hack about the new distro 
to include old Xorg packages and drivers.

 From that point of view, a fully open and supportable crap GPU starts 
to look appealing, since at least you get basic 2D accelerated 
primitives you can use - with a closed GPU you get just a dumb frame 
buffer device. Whether the difference is signifficant enough to matter, 
I don't know.

Gordan