svsematest - Man Page

Start two threads or fork two processes and measure the latency of SYSV semaphores

# SPDX-License-Identifier: GPL-2.0-or-later


svsematest [-a|--affinity NUM] [-b|--breaktrace USEC] [-d|--distance DIST] [-D|--duration TIME] [-f|--fork [OPT]] [-i|--interval INTV] [--json FILENAME] [-l|--loops LOOPS] [-p|--prio PRIO] [-q|--quiet] [-S|--smp] [-t|--threads [NUM]]


The program svsematest starts two threads or, optionally, forks two processes that are synchronized via SYSV semaphores and measures the latency between releasing a semaphore on one side and getting it on the other side.


-a,  --affinity[=NUM]

Run on processor number NUM. If PROC is not specified, run on current processor.

-b,  --breaktrace=USEC

Send break trace command when latency > USEC. This is a debugging option to control the latency tracer in the realtime preemption patch. It is useful to track down unexpected large latencies of a system.

-d,  --distance=DIST

Set the distance of thread intervals in microseconds (default is 500 us). When  cyclictest 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: Interval(thread N) = Interval(thread N-1) + DIST

-D,  --duration=TIME

Specify a length for the test run.
Append 'm', 'h', or 'd' to specify minutes, hours or days.

-f,  --fork

Instead of creating threads (which is the default), fork new processes

-i,  --interval=INTV

Set the base interval of the thread(s) in microseconds (default is 1000 us). This sets the interval of the first thread. See also -d.


Write final results into FILENAME, JSON formatted.

-l,  --loops=LOOPS

Set the number of loops. The default is 0 (endless). This option is useful for automated tests with a given number of test cycles. svsematest is stopped once the number of timer intervals has been reached.

-p,  --prio=PRIO

Set the priority of the process.

-q,  --quiet

Print a summary only on exit. Useful for automated tests, where only the summary output needs to be captured.

-S,  --smp

SMP testing: options -a -t and same priority of all threads

-t,  --threads[=NUM]

Set the number of test threads (default is 1, if this option is not given). If NUM is specified, create NUM test threads. If NUM is not specified, NUM is set to the number of available CPUs.


The following example was running on a 4-way CPU:

# svsematest -a -t -p99 -i100 -d25 -l1000000
#0: ID13110, P99, CPU0, I100; #1: ID13111, P99, CPU0, Cycles 1000000
#2: ID13112, P98, CPU1, I125; #3: ID13113, P98, CPU1, Cycles 813573
#4: ID13114, P97, CPU2, I150; #5: ID13115, P97, CPU2, Cycles 667285
#6: ID13116, P96, CPU3, I175; #7: ID13117, P96, CPU3, Cycles 591403
#1 -> #0, Min    1, Cur    2, Avg    2, Max   12
#3 -> #2, Min    1, Cur    3, Avg    2, Max   12
#5 -> #4, Min    1, Cur    3, Avg    3, Max   12
#7 -> #6, Min    1, Cur    2, Avg    3, Max   11


Carsten Emde <>

See Also