CONFIG PREEMPT RT Patch
The CONFIG_PREEMPT_RT Patch Set
The CONFIG_PREEMPT_RT patch set is maintained by a small group of core developers, led by Ingo Molnar. This patch allows nearly all of the kernel to be preempted, with the exception of a few very small regions of code ("raw_spinlock critical regions"). This is done by replacing most kernel spinlocks with mutexes that support priority inheritance, as well as moving all interrupt and software interrupts to kernel threads.
It further incorporates high resolution timers - a patch set, which is independently maintained.
You can find now a detailed RT_PREEMPT_HOWTO on this page.
Paul McKenney has written a good CONFIG_PREEMPT_RT overview which is a good introduction to the changes introduced to the kernel by the CONFIG_PREEMPT_RT patch.
There is also an apt repository for Ubuntu with x86 precompiled kernel. You can find more information in this wiki page:
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.
Platforms Tested and in Use with CONFIG_PREEMPT_RT
|Processor||Model #'s||Kernel version(s)||Contact(s)||Comment(s)|
|Opteron||IBM LS-20, LS-21, x3455||2.6.16-rt22, 2.6.20-rt8||Theodore Ts'o, Darren Hart|
|Xeon||IBM 6850-P4U||2.6.20-rt8, 2.6.21-rc6-rt0||Dave Sperry|
|P4||Compaq Evo N610||2.6.16-rt22||Dave Sperry|
|P3||Celeron 1300||184.108.40.206-rt14||Oleksandr Natalenko|
|Prescott||PentiumD 3 GHz||220.127.116.11-rt9||Dmitry Pisklov|
|Intel||Pentium 4 2.4 GHz||18.104.22.168-rt12||Jaswinder Singh|
|Intel||Pentium 4 2.8 GHz with HT||22.214.171.124-rt12||Jaswinder Singh|
|Intel||FSC D2151S Celeron D 2.93 Ghz||2.6.20-rt8||Remy Bohmer||Avg. latency < 10us, worst case latency: < 30us (see Note 1)|
|Intel||FSC D2151S Core 2 Duo E6300||2.6.20-rt8||Remy Bohmer||Avg. latency < 10us, worst case latency: < 30us (see Note 1)|
|Intel||Asus P5B Core 2 Duo E6600 2.4GHz||2.6.23-rc4-rt1||Remy Bohmer||Avg. latency < 10us, worst case latency: < 30us (see Note 1)|
|Intel||IBM Thinkpad T43 Pentium M CPU 2 GHz||2.6.23-rt3||PhilK||Avg. latency < 14us, worst case latency: < 32us|
|ARM9 (v4t)||Atmel AT91RM9200-EK (See AT91-Notes)||126.96.36.199-rt5||Remy Bohmer||worst case latency: < 500us (see Note 1)|
|ARM9 (v5t)||Atmel AT91SAM9261-EK (See AT91-Notes)||188.8.131.52-rt5||Remy Bohmer||worst case latency: < 500us (see Note 1)|
|ARM9 (v5tej)||TI OMAP5912 OSK||2.6.23-rt1||OMAP ML||A small additional OMAP specific patch on top of -rt is needed. See ML.|
|ARM9 (v5tej)||TI DM6446 DaVinci||2.6.23-rt1||DaVinci ML||A small additional DaVinci specific patch on top of -rt is needed. See ML.|
Note 1: latency is defined as the time between the moment an interrupt occurs in hardware, and the moment the corresponding interrupt-thread gets running.
AT91-Notes: The following issues are known on this architecture:
- Serial port (DBGU) driver does illegal calls in Interrupt context. The interrupt handler has to be split up. (Patch can be found at patch)
- Priority Inheritance Mutexes in userspace (PTHREAD_PRIO_INHERIT) only works since 2.6.23-rt1 with Glibc 2.5 and higher. Tested and stable with applications that match the memory locking scheme described on HOWTO:_Build_an_RT-application.
- Clocksource and clockevent implementations are available, and are in mainline since 2.6.24-rc4. (or see AT91-patchset) Tickless and HRT both work, but not using them due to very high CPU load compared to a ticking kernel on preempt-rt.
- GPIO Interrupt handling is not stable which causes missing GPIO interrupts, fixed by patch (Without this patch, the Ethernet adapter (DM9000) on AT91SAM9261-EK does not work in combination with PREEMPT-RT.)