Re: Realtime linux kernel on multicore processor

[Nivedita Singhvi <niv@us.ibm.com>]

Neel Mehta wrote:
> Hi. I have 2 computers with ubuntu:
> 1. Core 2 Duo - Non realtime linux kernel
> 2. Quad core - Realtime linux kernel
> 
> Both of them are using ubuntu. I am running a process that generates 2
> threads, both of which are continuously processing something.
> 1. On core 2 duo (normal kernel): both the cores are running above 90% load.
> 2. on quad core(realtime kernel): only one core runs above 90%, and
> the other cores are not at such a high load. The core which is on high
> load keeps on alternating among the 4 cores.
> 
> So, my question is why doesnt 2 cores run on high load on quad core?
> Is there a problem in multiprocessing in realtime linux kernel? Can
> someone guide me where the source of problem could be?

I'll start with the obvious - if the same amount of work is
being done, but now on a larger number of cores, the load on
each individual core could reduce (since you don't say what
else is contributing to the load on the system, etc).

As an example of this class of behavior, look at your irq distribution.
The rotation of the load sounds a lot like it's being driven by
interrupt round-robining, for instance.

thanks,
Nivedita