[Cbe-oss-dev] Call/return from PPE to SPE functions

[Julio M. Merino Vidal]

On 29/05/2007, at 20:56, Arnd Bergmann wrote:
>
> There are four different states that a context can be in:
>
> 1. saved and idle
> 2. saved and trying to run
> 3. loaded and running
> 4. loaded and idle
>
> Initially, it is in state 1, where you can easily modify the  
> registers.
> When you call spe_context_run, it goes through state 2 in the  
> scheduler
> to state 3, where it actually executes code.
>
> When it returns by the means of stop-and-signal, and there is no other
> context in state 2, it will be in state 4, waiting to be called again.
> This is an important performance optimization. When you call
> spe_context_run the next time, it can quickly go from state 4 to  
> state 3
> again, without ever having to be saved into memory.

Not exactly related to this, but I want to make sure I understood the  
code correctly.  Suppose a context A in state 4.  Then you put B1..BN  
contexts (where N = number of available SPUs) in state 3.  In that  
case, context A goes to state 1 until it can be rescheduled again  
(e.g. one of the Bi contexts terminates), at which point it is put in  
state 2 and later in state 3.  Right?

Thanks,

-- 
Julio M. Merino Vidal <jmerino at ac.upc.edu>