[Ksummit-discuss] [TECH TOPIC] Mainlining PREEMPT_RT

[Steven Rostedt]

On Wed, 14 Oct 2015 12:30:21 -0700
Tim Bird <tim.bird at sonymobile.com> wrote:

REPLY ALL Tim! I didn't notice this email till I saw it as QotW on LWN.


> Check out Xenomai. (xenomai.org)  I think that's what many embedded folk use
> if they find that RT-PREEMPT does not meet their needs.  Xenomai 3.0
> allows you to use their system either on top of RT-PREEMPT or
> on top of their Cobalt kernel sitting next to (or in front of,
> depending on your perspective) the Linux kernel.
> 
> Sony used RT-PREEMPT in some products, and a dual-kernel in others,
> and isolated CPUs running something else (usually uItron) in yet others.
> 
> Personally, I'd be happy to see RT-PREEMPT go in - there are certain use

BTW, it's PREEMPT_RT not RT-PREEMPT.

> cases for it.  I'd also like to see the NOHZ stuff go in as well.  It should
> solve a set of problems for isolating RT tasks without sacrificing
> performance on the non-RT CPUs.  And finally, I wouldn't mind putting
> a non-Linux RT kernel like Cobalt (oh the horrors) into mainline as well.
> Each of these approaches has their strengths and weaknesses.  Linux is,
> after all, whatever we say it is - and it could easily have a small RT
> micro-kernel as part of the source base as well.
> 
> AFAIK the patent issues that plagued the dual-kernel approach are now
> behind us, so this might be a good area of investigation.
> 
> I've long felt that RT-PREEMPT was sucking the oxygen out of getting other,
> technically valid, approaches to RT with Linux into mainline.

I'm perfectly fine with working together with Xenomai. When you need a
few microsecond latencies, that may be the best tool. I don't think
they are mutually exclusive, but actually complement each other quite
nicely.

-- Steve