Topics Overview for PREEMPT_RT mainlining

This page lists all the topics that need to be handled to get PREEMPT_RT mainlined since the RTL collaborative project started. The main reason for these changes is to simplify RT interaction and integration. The topics are split into different types. In addition to the topics listed, testing, documentation, and LTS kernel support for the PREEMPT_RT patch have to be done continuously.

• The CPU hotplug code needs an overhaul in general - Mostly done
• Some of the existing timer infrastructure needs to be rewritten - Initial problems solved, still work in progress
• Pagefault disable/enable handling (the kernel pagefault disable/enable mechanism is not RT compatible. Rework it to fit RT) - Done

• kmap infrastructure – adaption to make it RT compatible - Open item, no real benefit for mainline so it's postponed to the 'RT only section'
• Additional annotation mechanisms are necessary which allow RT to substitute functionality. (Such annotations are useful in general even for non-RT as they add value by making the code clearer and the scope of functionality documented) - Work in progress
• Extending debug infrastructure, e.g. lockdep to handle the new lock types. - Open item, partial issues solved

• Make use of the new annotation mechanisms
• Soft interrupt handling – structure must be adopted to be RT compatible
• Reader/writer lock handling - they are not scalable on RT. Find a scalable solution - Replacement exists but might need to be revisited
• Hotplug interaction – find a proper solution able to be compatible with RT requirements - Solved
• Timer interaction – rework the kernel architecture to be compatible with RT requirements - Partially solved, work in progress
• More palatable approach to RT friendly memory management - develop an upstream acceptable solution for the RT requirements - work in progress

Various details which do not fit into any of the above categories, but need to be addressed to make RT upstream acceptable

• Required to make mainline developers comfortable with it
• Required for driver developers