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Benchmark and comparison of real-time solutions based on embedded Linux Benchmark and comparison of real-time solutions based on embedded Linux Peter Feuerer August 8, 2007

Benchmark and comparison of real-time solutions based on embedded Linux Table of contents General Motivation Real-time computing Preparations Environment setup Open Realtime Framework Benchmarks Interrupt latency Jitter Maximal frequency Inter-process communication Overload behavior Priority functionality Conclusion

Benchmark and comparison of real-time solutions based on embedded Linux General Motivation Motivation To enhance Linux by real-time ability there are ◮ different real-time approaches and ◮ different hardware platforms. When specifying the system for a particular application one real-time approach and one hardware must be chosen. → A benchmark is needed.

Benchmark and comparison of real-time solutions based on embedded Linux General Real-time computing What is real-time? A real-time capable system ◮ is reliable ◮ has deterministic behaviour and ◮ is able to adhere to specified deadlines. There are two main real-time categories: ◮ Soft real-time - would be great to adhere to deadlines. ◮ Hard real-time - not allowed to miss any deadline.

Benchmark and comparison of real-time solutions based on embedded Linux General Real-time computing Linux real-time approaches Rtai: ◮ One of the first approaches. ◮ Dual kernel. ◮ Real-time applications in kernel-space. Xenomai: ◮ Dual kernel. ◮ Skin support, e.g. Posix API, VxWorks API. ◮ Real-time applications in user- and kernel-space. Rt-Preempt: ◮ Patch to make vanilla Linux kernel real-time capable. ◮ Real-time applications run in user-space.

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Environment setup Overview To get meaningful results from a practical point of view, this setup is used:

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Environment setup Target setup Intel x86: ◮ Hardware: AMD k7 600Mhz desktop PC, Kontron Geode gx1 embedded system. ◮ Software: modified ArchLinux distribution, Linux kernel 2.6 and 2.4 with Rtai, Xenomai and a rt-preempt patched 2.6 kernel PowerPC: ◮ Hardware: MEG32 from Frenco ◮ Software: ELDK toolchain and Linux kernel 2.6 and 2.4 with Xenomai and kernel 2.4 with Rtai ARM: ◮ Hardware: LILLY-9xx board from Incostartec. ◮ Software: skipped, due to missing patches of the real-time extensions.

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Environment setup Measurement USB-Scope Mephisto UM202: ◮ C-API and library to write custom measurement applications ◮ Windows application with GUI to monitor and control

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Open Realtime Framework What is ORF? The Open Realtime Framework is an open source project initiated and developed by Yellowstone-Soft. ◮ Standardized API for real-time applications ◮ Platform independent and portable ◮ Cyclical working sequential controls like a Siemens PLC has ◮ Modular design

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Open Realtime Framework ORF enhancement: Dynamical linked libraries To enable addition and removal of real-time programs without stopping ORF, programs are built as libraries and loaded dynamically. Changes to ORF: ◮ Management for the loaded libraries ◮ Functionality for linking and unlinking ◮ Modification to ”orf add initfunc” and ”orf delete initfunc” functions to not conflict with ORF spec.

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Open Realtime Framework ORF enhancement: Character devices The former communication between ORF and user-space was done by Rtai FIFOs. → platform dependent. Standard kernel device files has been implemented: ◮ Former Rtai FIFOs has been removed ◮ /dev/rtf[0-X] is handled by main ORF module ◮ One communication cycle: 1. User-space application writes command 2. ORF processes command and blocks user-space application 3. User-space application reads result

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Open Realtime Framework ORF enhancement: I/O-API To create meaningful benchmarks from a practical point of view I/O-port access is needed. An I/O-API within ORF enables platform independent usage. It consists of four functions: init-io to initialize the I/O-port reset-io to reset the I/O-port outb writes data inb reads data

Benchmark and comparison of real-time solutions based on embedded Linux Preparations Open Realtime Framework ORF enhancement: Interrupt handling Catching interrupts was not implemented in ORF yet. ◮ Special interrupt ”threads” have been added to ORF to meet ORF’s specs ◮ Interrupt service routine wrappers are introduced ◮ ORF real-time progs add their main function to the interrupt wrapper

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Interrupt latency Interrupt latency Idea: ◮ I/O-pin is set high level → interrupt is created ◮ ORF program catches interrupt and sets pin back to low ◮ Duration of high level phase is measured

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Interrupt latency Results: Interrupt latency ◮ Blue: system is idling ◮ Red: system is under heavy load

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Jitter Jitter Idea: ◮ ORF program creates square-wave ◮ Scope application measures durations ◮ Maximal jitter is calculated

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Jitter Results: Jitter

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Maximal frequency Maximal Frequency Idea: ◮ Alive square-wave signal on pin 2 ◮ Square-wave signal with rising frequency on pin 1 ◮ Measurement application calculates frequency of pin 1 ◮ Maximal frequency is stored if no malfunction appeared ◮ Measurement stops if alive signal or frequency signal gets lost

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Maximal frequency Results: Maximal Frequency

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Inter-process communication Inter-process communication Idea: ◮ ”Echo” function implemented into ORF ◮ writes received data back ◮ counts packages ◮ Infinite amount of packages are written to the character device file ◮ ORF real-time program prints amount of transmitted packages every second

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Inter-process communication Results: Inter-process communication

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Overload behavior Overload behavior Idea: ◮ 2 threads, one with high frequency, one with lower frequency ◮ A shot of the lower frequent thread produces short-time overload ◮ Two scenarios: ◮ light overload - period of high frequent thread is delayed ◮ heavy overload - period of high frequent thread is omitted

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Overload behavior Results: Overload behavior ppc / 2.6 / xn x86 / 2.6 / xn x86 / 2.6 / rtai test1 test2 test1 test2 test1 test2 . No load X - X - X - Heavy load X - X - o - x86 / 2.4 / rtai test1 test2 No load X - Heavy load o - X: test passed -: test aborted o: machine died

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Priority functionality Priority functionality Idea: ◮ 4 threads with different priority and frequency ◮ Every thread sets its output pin to high, when active ◮ Measurement application checks preemption

Benchmark and comparison of real-time solutions based on embedded Linux Benchmarks Priority functionality Results: Priority functionality The result contains the amount of how often each thread has been preempted by any other thread. Linux 2.6 + Xenomai: No load Heavy load T0 T1 T2 T3 T0 T1 T2 T3 T0 0 0 0 0 0 0 0 0 T1 932 0 0 0 903 0 0 0 T2 922 104 0 0 925 98 0 0 T3 4480 486 40 0 4531 503 48 0

Benchmark and comparison of real-time solutions based on embedded Linux Conclusion Conclusion The benchmark suite created in this project can be used to do meaningful evaluations of real-time approaches on various platforms. Rtai: ◮ very deterministic, high performance ◮ overload must be avoided Xenomai: ◮ stable in case of overloads ◮ state of the art technology ◮ skin support Rt-Preempt: ◮ in the very beginning ◮ hard-real-time capability

Benchmark and comparison of real-time solutions based on embedded Linux Questions & Answers Questions?