Real Time in Embedded Linux System
From IGEP - ISEE Wiki
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
