Hello all, Please give contribution with open heart and give answers to max questions as possible and give your reviews : 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 A1 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 http://www.kernel.org/pub/linux/kernel/projects/rt/ then related get vanilla kernel from http://kernel.org then patch , configure and compile Section 2 - Architecture questions Q1 Which Architecture are supporting realtime and who is maintainer A1 Q2 What is the procedure to support realtime in new architecture A2 Section 3 - Mailing list questions Q1 realtime mailing list and archives A1 http://www.mail-archive.com/linux-rt-users@xxxxxxxxxxxxxxx/ 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 A2 Section 4 - Realtime Patches questions Q1 Why I need to download realtime patches, If realtime support is in Linux kernel A1 Q2 Download latest realtime patches A2 http://www.kernel.org/pub/linux/kernel/projects/rt/ 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. Section 5 - Configuring/compiling questions Q1 How to enable/disable realtime support A1 Q2 Change realtime support run time or statically A2 Q3 Required parameters for configuring realtime kernel A3 Q4 Optional parameters for configuring realtime kernel, but they effect realtime performance A4 Section 6 - Realtime samples/Performance questions Q1 What effects by realtime support and how much and samples to test it and who maintains these samples a. scheduling, task switching time b. Interrupt latency c. Interprocess communication d. Filesystem e. Device drivers f. Network g. X-Windows Section 7 - Realtime Applications questions Q1 List of realtime APIs A1 Q2 How to write realtime applications A2 Q3 Which programming languages are suitable for writing realtime applications A3 Q4 Keep following things in mind while writing realtime applications A4 Taking care of the following during the initial startup phase: * Call directly from the main() entry the mlockall() call. * Create all threads at startup time of the application, and touch each page of the entire stack of each thread. Never start threads dynamically during RT show time, this will ruin RT behavior. * Never use system calls that are known to generate pagefaults, such as fopen(). (Opening of files does the mmap() system call, which generates a page-fault). * Do not use 'compile time static arrays' without initializing them directly after startup, before RT show time. Q5 Do I need to recompile my applications to get realtime performance A5 Section 8 - Maintainers questions Q1 Maintainers of realtime kernel patch A1 On 9/29/07, Jaswinder Singh <jaswinderlinuxrt@xxxxxxxxx> wrote: > hello all, > > I made sections in FAQ to make it more readable. > > Thank you, > > Jaswinder Singh. > - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
