Re: AMP on an SMP system

[Michael Schnell <mschnell@lumino.de>]

On 08/02/2013 01:42 PM, Robert Schwebel wrote:
> Before hacking around (which might also lead to interesting solutions),
> I would start using a kernel with preempt-rt support and play with the
> cpu affinity:
>
> http://lxr.linux.no/#linux+v3.10.4/Documentation/kernel-parameters.txt#L1257
>

Robert !
Nice to see you here (I do own your "Embedded Linux Handbuch für 
Entwickler" :-) )

Thanks for the pointer !

I do already know "preempt-rt", but I was not aware of cpu affinity.

So this might help.

In fact I need a way to do very guaranteed low latency. regarding the 
high clock rate (about 1 GHz) modern ARM chips can provide, maybe 
preempt-rt with the cpu affinity might be a decent way to go.

The raining questions include
  - how to calculate the maximum latency that can be guaranteed ? (i.e. 
does the Kernel impose any spinlocks and interrupt disables on the would 
be AMP subsystem ?)
  - how to assign an interrupt (e.g. a dedicated timer) to the subsystem ?
  - Do the interrupts immediately call the ISR of the cpu "under 
affinity" or is some additional latency imposed by the Kernel (and how 
many cpu cycles at max are needed to enter the ISR) ?

Thanks,
-Michael