[K42-discussion] Re: Possible benefit of running K42 on Cell CBE ...

[Jimi Xenidis]

I'm not sure I understand your questions here.
But here it goes.
My sizings assumes the work is done by people who are quite familiar  
with Linux and K42.

On Dec 21, 2005, at 10:44 AM, Elvis John Dowson wrote:

> Hi Jimi,
>            What kind of functionality would a K42 SPU Linux Module  
> contain,
> vis-a-vis the standard K42 PPU Linux Module ?

Assuming you are asking about the work in the Linux Kernel module we  
link into k42.
If you just wanted to run K42 on the PPE the you could easily write  
(or backport) the handful of code to make this happen, specifically  
the handling of the IIC is the only concern I can think of.

If you wanted SPU support then you would have to take the LinuxBPA  
changes en-masse and update our k42 to use the newer kernel code.   
Linux is a moving target, so _after_ the current update is complete  
(which is a background task for us) it may be another few weeks or  
few months.

Another concern is that user apps (the PU component) communicate with  
the SPU via Linux sysfs.  K42 does not normally use sysfs, so this  
would take a few weeks to get that interchange correct.

>
> How big would it be and what is the bare minimum set of  
> functionality that
> is needed to run the K42 SPU Linux Module kernel on a CBE SPU ?

To me "minimum" is:
  - load an SPU elf image on an SPU
  - Start the SPU
  - Detect when it is finished
  - dump result

This could be a week-or-2, if you wrote all new code for k42. but  
beyond that it is not very interesting.
I assume you are looking for a tighter coupling of the PU-task and  
the SPU-workload.
>
> What would the estimated size of a port of the K42 SPU Linux Kernel  
> module
> be, keeping in mind that there is only 256kb of local storage  
> available per
> SPE ?

I think I addressed this above, but I have no clue what the size of  
LS has to do with it.

>
> Is there some way to minimize the usage of SPU local storage by  
> virtualizing
> the SPU using the PPU and just incorporating minimal support for  
> the SPU,
> within the K42 PPU Linux Kernel, just to facilitate DMA transfers  
> of program
> and data using the SPE Memory Flow Controller (MFC) ?  Wouldnt that  
> level of
> support be sufficient support for the SPU by the K42 OS ?
>

I have no clue what you are asking hear, but as far as minimal  
support, I think I addressed that above.