After a two years long break the Summit on a Summit was back in early June this year. As always, the event was organized by Christoph Hellwig, Daniel Wagner and our own Richard Weinberger. It took place at the Glungezerhütte at almost 2600 m altitude in the heart of Tuxer Alps in Tyrol, Austria. As usual hot topics around implementing realtime features on Linux were discussed. Beside of PREEMPT_RT many of discussions focused this time on Xenomai.
On Friday we met at Innsbruck train station and drove up to Tulfes where we enjoyed a traditional Austrian lunch at the Tuxerbauer. Hiking up to the Glungezerhütte took only a few hours and due to foggy weather it wasn’t too hot. Up at the lodge the sun came out and we had perfect weather until Sunday when we hiked down to Tulfes. This allowed among heated discussions also some nice hikes to the nearby summits such as the Sonnen- and Viggarspitze.
This year many discussed topics orbited around solving maintenance and upgrade problems - especially the Xenomai project suffers from that. The transition to the new interrupt pipeline implementation, Dovetail will hopefully reduce the overhead but it isn’t a silver bullet. PREEMPT_RT wise, recent regressions and subtle behavioral changes have been discussed. Most notably changes to softirq processing which made meeting timing constraints for networking application more difficult. The possibility of using XDP and eBPF was stormily debated, bypassing most of Linux’ network stack seems also for time sensitive applications a desirable solution. But it comes with a cost: more complexity and critical code in the application itself. Other topics focused on minor problems such as trouble with the cgroup memory controller and eBPF centered workloads on PREEMPT_RT. Xenomai folks also took the chance to present their realtime capable serial drivers after a PREEMPT_RT user complained about tty drivers and timing sensitive workloads on Linux. Interestingly, eBPF came up on most discussions, sometimes as solution, sometimes as root cause of trouble. At the end of the event we had a good mix of community, user facing features and deeply internal related topics.