1Cyclictest is a program to test the performance of high-resolution timers on Linux systems. 2 3Installation 4 5Get the latest source tarball, untar into a directory of your choice and run make in the source directory. 6 7You can run the resulting binary from there or install it. 8 9Run it 10 11Make sure to be root or use sudo to run cyclictest. 12 13Without parameters cyclictest creates one thread with a 1ms interval timer. 14 15cyclictest -h provides help text for the various options 16 -b USEC --breaktrace=USEC send break trace command when latency > USEC 17 -c CLOCK --clock=CLOCK select clock 18 19 0 = CLOCK_MONOTONIC (default) 20 1 = CLOCK_REALTIME 21 22 -d DIST --distance=DIST distance of thread intervals in us default=500 23 -i INTV --interval=INTV base interval of thread in us default=1000 24 -l LOOPS --loops=LOOPS number of loops: default=0(endless) 25 -n --nanosleep use clock_nanosleep 26 -p PRIO --prio=PRIO priority of highest prio thread 27 -q --quiet print only a summary on exit 28 -r --relative use relative timer instead of absolute 29 -s --system use sys_nanosleep and sys_setitimer 30 -t NUM --threads=NUM number of threads: default=1 31 -v --verbose output values on stdout for statistics 32 33format: n:c:v n=tasknum c=count v=value in us 34 35The -b optionis a debugging option to control the latency tracer in the realtime 36preemption patch. It is useful to track down unexpected large latencies on a system. 37This option only works with: 38 39 * CONFIG_PREEMPT_RT=y 40 * CONFIG_LATENCY_TIMING=y 41 * CONFIG_LATENCY_TRACE=y 42 43kernel configuration options enabled. The USEC parameter to the -b option defines 44a maximum latency value, which is compared against the actual latencies of the test. 45Once the measured latency is higher than the given maximum, the kernel tracer and 46cyclictest is stopped. The trace can be read from /proc/latency_trace: 47 48 mybox# cat /proc/latency_trace >trace.log 49 50Please be aware that the tracer adds significant overhead to the kernel, so the 51latencies will be much higher than on a kernel with latency tracing disabled. 52 53 Using -c CLOCK selects the clock, which is used 54 55 * 0 selects CLOCK_MONOTONIC, which is the monotonic increasing system time. 56 This is the default selection 57 * 1 selects CLOCK_REALTIME, which is the time of day time. 58 59CLOCK_REALTIME can be set by settimeofday, while CLOCK_MONOTONIC can not be 60modified by the user. 61 62This option has no influence when the -s option is given. 63 64-d DIST set the distance of thread intervals in microseconds (default is 500us) 65 66When cylictest is called with the -t option and more than one thread is created, then this distance value is added to the interval of the threads. 67 68Interval(thread N) = Interval(thread N-1) + DIST 69 70-i INTV set the base interval of the thread(s) in microseconds (default is 1000us) 71 72This sets the interval of the first thread. See also -d. 73 74-l LOOPS set the number of loops (default = 0(endless)) 75 76This option is useful for automated tests with a given number of test cycles. cyclictest is stopped once the number of timer intervals has been reached. 77 78-n use clock_nanosleep instead of posix interval timers 79 80Setting this option runs the tests with clock_nanosleep instead of posix interval timers. 81 82-p PRIO set the priority of the first thread 83 84The given priority is set to the first test thread. Each further thread gets a lower priority: 85 86Priority(Thread N) = Priority(Thread N-1) 87 88-q run the tests quiet and print only a summary on exit 89 90Useful for automated tests, where only the summary output needs to be captured 91 92-r use relative timers instead of absolute 93 94The default behaviour of the tests is to use absolute timers. This option is there for completeness and should not be used for reproducible tests. 95 96-s use sys_nanosleep and sys_setitimer instead of posix timers 97 98Note, that -s can only be used with one thread because itimers are per process and not per thread. -s in combination with -n uses the nanosleep syscall and is not restricted to one thread 99 100-t NUM set the number of test threads (default is 1) 101 102Create NUM test threads. See -d, -i and -p for further information. 103 104-v output values on stdout for statistics 105 106This option is used to gather statistical information about the latency distribution. The output is sent to stdout. The output format is 107 108n:c:v 109 110where n=task number c=count v=latency value in us 111 112Use this option in combination with -l 113 114The OSADL Realtime LiveCD project (http://www.osadl.org/projects-live-cd.0.html) provides a script to plot the latency distribution. 115