[atlas] Turris Omnia as probe Platform?

Hi!

On Sat, Dec 5, 2015 at 6:02 PM, João Damas <joao at bondis.org> wrote:
> What you want from the probe is predictability in the form of minimal 
> jitter and possibly some calibration (to equate latency). IF the 
> Turris people can run the Atlas code with some sort of real-time 
> scheduling then it is going to be OK as a probe. Can they?

It depends on what level of control you need. The board will be 
supported by vanilla Linux kernel (we are almost there). So you/we can 
compile in whatever is needed.

The hardware should be more than enough for routing (=processing input 
IRQs from NICs and forwarding) and almost everything else can be 
prioritized. But I suppose we need to discuss that into more detail to 
address all possible interactions. Is there some documentation of 
kernel tuning in the current probes?

And the probe could perform self-tests periodically and disable itself 
either temporarily or permanently if the router fails the test.

> 
> 
> If it is a process competing with whatever else the router might be 
> doing at the time then I agree, it wouldn’t be suitable as a probe 
> for things that involve precise time measurements, although they 
> could still run the set of measurements for which precise timing is 
> not necessary (routing, DNS, etc). In the Atlas probe all software is 
> under control of one party and *I guess* doesn’t interfere with the 
> rest of the software running on them.

I personally (though I am the Turris kernel guy) think that we can 
cooperate on determining interactions and tune the basic system for the 
probe, if needed. But I suppose that we won't be shipping the routers 
with the probe turned on by default anyway.

 From my point of view it would make sense to do more general work in 
this direction. It boils down to the question whether we can have the 
probe in form of a daemon? Of course there have to be some requirements 
for reliable operation, that can be enforced on the OS side and checked 
on the daemon side. But it does not make sense to think of them if the 
software probe is still deemed undesirable. Is it?

Tomas