Frequently Asked Questions

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Quetions are given by:
Questions are given by:
[[User:jaswinderlinuxrt | Jaswinder Singh]]
[[User:jaswinderlinuxrt | Jaswinder Singh]]

Revision as of 15:02, 29 September 2007




Questions are given by:

Jaswinder Singh

Answers are given by:


Revision History
Revision 1 2007-09-29
Draft / Work in progress


FAQ for realtime support in Linux Kernel


Question Index

1. Realtime Support questions

2. Architecture questions

3. Mailing list questions

4. Realtime Patches questions

5. Configuring/compiling questions

6. Realtime samples/Performance questions

7. Realtime Applications questions

8. Maintainers questions

Section 1 - Realtime Support questions

Q1: What is realtime support


Q2: How realtime works

A2: The RT-Preempt patch converts Linux into a fully preemptible kernel. The magic is done with:

  • Making in-kernel locking-primitives (using spinlocks) preemptible though reimplementation with rtmutexes:
  • Critical sections protected by i.e. spinlock_t and rwlock_t are now preemptible. The creation of non-preemptible sections (in kernel) is still possible with raw_spinlock_t (same APIs like spinlock_t)
  • Implementing priority inheritance for in-kernel spinlocks and semaphores. For more information on priority inversion and priority inheritance please consult Introduction to Priority Inversion
  • Converting interrupt handlers into preemptible kernel threads: The RT-Preempt patch treats soft interrupt handlers in kernel thread context, which is represented by a task_struct like a common userspace process. However it is also possible to register an IRQ in kernel context.
  • Converting the old Linux timer API into separate infrastructures for high resolution kernel timers plus one for timeouts, leading to userspace POSIX timers with high resolution.

Q3: What is the procedure to add realtime support

A3: Download latest realtime preemption patch from then get related vanilla kernel from then patch, configure and compile

Section 2 - Architecture questions

Q1: Which Architecture are supporting realtime and who is maintainer


Q2: What is the procedure to support realtime in new architecture


Section 3 - Mailing list questions

Q1: realtime mailing list and archives


Q2: If I have some doubts or problems regarding realtime, do I need to send mail in realtime mailing list or linux kernel mailing list or both


Section 4 - Realtime Patches questions

Q1: Why I need to download realtime patches, If realtime support is in Linux kernel


Q2: Download latest realtime patches


Q3: Where can I post my realtime patches

A3: Please send patches for the CONFIG_PREEMPT_RT Patch Set to LKML and put Ingo Molnar and Thomas Gleixner on CC.

Please do not send clocksource and clockevents related patches against the -rt patch. Make sure they apply against the latest -hrt-dyntick patch. -hrt-dyntick might be a bit ahead of -rt at times, but the -rt patch pulls -hrt-dyntick on a regular base.

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