Re: ARINC653

[Dario Faggioli <dario.faggioli@citrix.com>]

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On lun, 2013-12-09 at 20:23 +0000, Simon Martin wrote:
> smartin@smartin-xen:~/projects/trio/xen/pv499$ sudo xl cpupool-list
> Name               CPUs   Sched     Active   Domain count
> Pool-0               3    credit       y          1
> pv499                1  arinc653       y          1
>
Ok, which pcpus are in each pool? In theory, it shouldn't matter, but,
you know... :-P
 
> After loading the domU into the pv499 and running the program that
> configures the arinc scheduler I get this:
>  
> smartin@smartin-xen:~/projects/trio/xen/pv499$ sudo xl list
> Name                                        ID   Mem VCPUs      State
> Time(s)
> Domain-0                                     0  2967     4     r-----
> 117.2
> pv499                                       24    32     1     r-----
> 373.0
>  
> So far so good. Now looking at the timings things are not too
> different from when I was using the credit scheduler. Running a single
> shot timer at a period of 250 µs gives me a jitter in the timer
> handler latency in the range [3.5 µs, 45 µs]. This makes it look like
> the problem in the jitter is not the scheduling but the underlying
> hypervisor. It is going off to do things on this CPU which is causing
> the deadlines not to be met.
>  
> So unless I am doing something silly it looks like I will have to go
> to RT-Xen to get better timings. For the moment I'm going to leave
> this and go on to getting more of my operating system working.
>
Well, RT-Xen is a great project, but it's mostly, if not all, about
scheduling. I mean, all they do is introducing two new schedulers (with
a couple of operational mode in each), and that's it... There is nothing
there being done for reducing latency or jitter.

I think, we'd better off (as soon as, as you said, you have more pieces
in place), trying to figure out what is causing the behavior you're
seeing and workaround/fix/amend it!

It's a busy period, with the 4.4 release, etc., but, as repeatedly said,
I'm up for helping with this, if help is needed! :-P

Regards,
Dario

-- 
<<This happens because I choose it to happen!>> (Raistlin Majere)
-----------------------------------------------------------------
Dario Faggioli, Ph.D, http://about.me/dario.faggioli
Senior Software Engineer, Citrix Systems R&D Ltd., Cambridge (UK)


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