[LITMUS^RT] Question about how to specify dedicated cores to G-EDF and the relative deadline

[Glenn Elliott]

On Dec 13, 2013, at 11:00 PM, Luo, Zheng <luozheng at wustl.edu> wrote:

> Hi everyone,
> 
> I have a question about how to choose dedicated group of cores on Litmus running G-EDF. For example, if my machine have 4 cores, I want to reserve core 0 for the Operating system, and core 1-3 to the rt-thread which can do the work. How can I do that? I tried the C-EDF, however used the L1,L2,L3 caches to do the division. I was wondering how can I do the division manually in the G-EDF?
> 
> Also, I have a question about the relative deadline, I think the normally the G-EDF should have the absolute deadline. Does the Litmus automatically convert relative deadline to the absolute deadline when using the G-EDF?
> 
> Thanks, Looking forward to the reply.    
> 
> 
> Zheng Luo

Hi Zheng,

I think you can accomplish what you want to do by using a “Release Master”.  This is enabled by asserting the CONFIG_RELEASE_MASTER compile-time option under the “Scheduling” menu.  This will reserve CPU0 (aka the “Release Master”) for handling release interrupts for G-EDF running on the remaining CPUs.  You can also run general code on the release master CPU, assuming you have properly configured CPU affinity masks for those processes/threads.

All EDF schedulers, including G-EDF, always uses a job’s absolute deadline to prioritize scheduling.  A relative deadline (a task attribute, not a job attribute) scheduler would be something like Deadline-Monotonic scheduling— tasks with smaller relative deadlines have higher priority.  Implementing your own Deadline-Monotonic scheduler is not hard.  There are kludgey ways to do it in Litmus with just 5 to 10 minutes of coding.

-Glenn
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