Difference between revisions of "Real Time in Embedded Linux System"
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== Real-time - Timers and scheduling latency == | == Real-time - Timers and scheduling latency == | ||
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=== Testing the Xenomai scheduling latency === | === Testing the Xenomai scheduling latency === | ||
+ | $ wget http://download.gna.org/xenomai/stable/xenomai-2.6.0.tar.bz2 | ||
+ | |||
+ | === rt-tests === | ||
+ | |||
+ | $ git clone git://github.com/clrkwllms/rt-tests.git | ||
− | + | == Links == | |
+ | |||
+ | * Tools to ensure a system's realtime capabilities | ||
+ | ** https://www.osadl.org/Single-View.111+M52212cb1379.0.html | ||
+ | ** https://www.osadl.org/Realtime-Preempt-Kernel.kernel-rt.0.html | ||
+ | ** https://www.osadl.org/Driver-to-Program-Signal-Tester.driver-to-program-signal-tester.0.html | ||
+ | ** https://www.osadl.org/Latency-generator.latency-generator.0.html | ||
+ | ** https://www.osadl.org/Visualize-the-temporal-relationship-of-L.taks-visualizer.0.html | ||
+ | * Other resources | ||
+ | ** https://www.osadl.org/fileadmin/dam/rtlws/12/Brown.pdf | ||
+ | ** http://embedded.communities.intel.com/servlet/JiveServlet/download/4435-1248/xeno_intel.pdf |
Revision as of 18:16, 8 November 2011
Contents
Real-time - Timers and scheduling latency
Based on free training materials from Free Electrons covering real-time (http://free-electrons.com/docs/realtime/)
Learn how to handle real-time processes and practice with the different real-time modes. Measure scheduling latency.
Setup
Using high-resolution timers
Have a look at the rttest.c source file
Now compile this program:
# gcc -o rttest rttest.c -lrt
Execute the program on the board
Testing the non-preemption kernel
Testing the voluntary preemption kernel
Recompile your kernel with CONFIG_PREEMPT_VOLUNTARY enabled and test the program with nothing special
Test the program with nothing special
# ./rttest Clock resolution (ns): 1 Measurement, please wait 1 minute... Samples: 153046 Min latency: 113 us Max latency: 7712 us Average latency: 292 us
Test your program and at the same time, add some workload to the board, by running
# stress --cpu 1 --io 2 --vm 2 --vm-bytes 128M --timeout 120s & # ./rttest Clock resolution (ns): 1 Measurement, please wait 1 minute... Samples: 90233 Min latency: 83 us Max latency: 28586 us Average latency: 558 us
Test your program again with the workload, but by running the program in the SCHED_FIFO scheduling class at priority 99
# stress --cpu 1 --io 2 --vm 2 --vm-bytes 128M --timeout 120s & # chrt -f -r 99 ./rttest Clock resolution (ns): 1 Measurement, please wait 1 minute... Samples: 210637 Min latency: 52 us Max latency: 2219 us Average latency: 181 us
Testing the preemptible kernel
Recompile your kernel with CONFIG_PREEMPT enabled and test the program with nothing special
# ./rttest Clock resolution (ns): 1 Measurement, please wait 1 minute... Samples: 154210 Min latency: 113 us Max latency: 9085 us Average latency: 288 us
Test your program and at the same time, add some workload to the board, by running
# stress --cpu 1 --io 2 --vm 2 --vm-bytes 128M --timeout 120s & # ./rttest Clock resolution (ns): 1 Measurement, please wait 1 minute... Samples: 113158 Min latency: 83 us Max latency: 15921 us Average latency: 421 us
Test your program again with the workload, but by running the program in the SCHED_FIFO scheduling class at priority 99
# stress --cpu 1 --io 2 --vm 2 --vm-bytes 128M --timeout 120s & # chrt -f -r 99 ./rttest Clock resolution (ns): 1 Measurement, please wait 1 minute... Samples: 235302 Min latency: 83 us Max latency: 296 us Average latency: 150 us
Testing the Xenomai scheduling latency
$ wget http://download.gna.org/xenomai/stable/xenomai-2.6.0.tar.bz2
rt-tests
$ git clone git://github.com/clrkwllms/rt-tests.git
Links
- Tools to ensure a system's realtime capabilities
- https://www.osadl.org/Single-View.111+M52212cb1379.0.html
- https://www.osadl.org/Realtime-Preempt-Kernel.kernel-rt.0.html
- https://www.osadl.org/Driver-to-Program-Signal-Tester.driver-to-program-signal-tester.0.html
- https://www.osadl.org/Latency-generator.latency-generator.0.html
- https://www.osadl.org/Visualize-the-temporal-relationship-of-L.taks-visualizer.0.html
- Other resources