Here are a few frequently asked questions about Cyclictest.

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

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 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]