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Cyclictest
Cyclictest is a high resolution test program originally written by Thomas Gleixner (tglx). A lot of people contributed to it later on and it is currently being maintained by Clark Williams and John Kacur.
Explanation
cyclictest runs a non real-time master thread which starts a defined number of measuring threads with a defined real-time priority. The measuring threads are woken up periodically with a defined interval by an expiring timer (cyclic alarm). Subsequently, the difference between the programmed and the effective wake-up time is calculated and handed over to the master thread via shared memory. The master thread tracks the latency values and prints the minimum, maximum and average for the latency once the number of iterations specified is completed.
Installation
Get the latest sources from the git repository, and clone the repository or fetch a released tarball from the archive, untar into a directory of your choice and run make in the source directory. If you want to cross compile, just run make CROSS_COMPILE=<your-compiler-prefix> (for example make CROSS_COMPILE=arm-v4t-linux-gnueabi-).
You can run the resulting binary from there or install it:
#> git clone git://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git #> cd rt-tests #> make all #> cp ./cyclictest /usr/bin/ #> cyclictest --help
libnuma is required to build cyclictest. Usually, it's safe to have libnuma installed also in non-numa systems, but if you don't want to install the numa libs (e.g. in embedded environment) then compile with make NUMA=0.
Run it
Make sure to be root or use sudo to run cyclictest.
Without parameters cyclictest creates one thread with a 1ms interval timer.
cyclictest -h provides help text for the various options.
More information is available by running man ./src/cyclictest/cyclictest.8. The OSADL Realtime LiveCD project provides a script to plot the latency distribution.
Expected Results
TODO: Run all the tests run in Expected results section of https://rt.wiki.kernel.org/index.php/Cyclictest and update here. We need to rerun the tests because they were run in 2006 on a Pentium III system running 2.6.16 kernel. Things have probably changed a bit now. :)
FAQ
ps shows the wrong scheduling class SCHED_OTHER
Each cyclictest-task consist of one or more threads. ps -ce shows only the main-process not the threads of the main-process. ps -eLc | grep cyclic shows the main-process an the containing threads with the correct scheduler class SCHED_FIFO.
#>./cyclictest -t5 -p 80 -n -i 10000 #> ps -cLe | grep cyclic 4764 4764 TS 19 pts/1 00:00:01 cyclictest 4764 4765 FF 120 pts/1 00:00:00 cyclictest 4764 4766 FF 119 pts/1 00:00:00 cyclictest 4764 4767 FF 118 pts/1 00:00:00 cyclictest 4764 4768 FF 117 pts/1 00:00:00 cyclictest 4764 4769 FF 116 pts/1 00:00:00 cyclictest
chrt shows the wrong scheduling class SCHED_OTHER
Don't use the PID of the main-process, but the pid of one of the threads from the main-process. The threads are shown with ps -cLe | grep cyclic.
#> chrt -p 4766 pid 4766's current scheduling policy: SCHED_FIFO pid 4766's current scheduling priority: 79
taskset for CPU affinity
taskset command is Written by Robert M. Love. SMP operating systems have choices when it comes to scheduling processes: a new or newly rescheduled process can run on any available cpu. However, while it shouldn't matter where a new process runs, an existing process should go back to the same cpu it was running on simply because the cpu may still be caching data that belongs to that process. This is particularly apt to be true if the process is a thread: the other threads in the same program are very likely to have cpu cache of interest to their brethren (though obviously this also diminishes the performance gain that might be seen from multithreading) . For these reasons, scheduling algorithms pay attention to cpu affinity and try to keep it constant. It is possible to force a process to run only on a certain cpu. There are Linux system calls (sched_setaffinity and sched_getaffinity) and a command line “taskset”.
#> taskset -c 3 top #> taskset -p [pid]
Compile failure because numa.h can't be found
make cc -D VERSION_STRING=0.85 -c src/cyclictest/cyclictest.c -Wall -Wno-nonnull -O2 -DNUMA -D_GNU_SOURCE -Isrc/include In file included from src/cyclictest/cyclictest.c:37:0: src/cyclictest/rt_numa.h:23:18: fatal error: numa.h: No such file or directory compilation terminated. make: *** [cyclictest.o] Error 1
Simply install your distribution's numa development package. On Fedora this is numactl-devel, so
su -c 'yum install numactl-devel'
This is only required for building. This will not affect the way the test runs on non-numa machines
External Links
Current repo
Clone one of the following
- git://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git
rt-tests tarballs
Mailing List
