Infoportal
Inhaltsverzeichnis
Cyclictest
The Cyclictest starts several tasks, which are called periodically. The effective period duration is measured and the jitter is displayed.
A presentation from the „Embedded Linux Conference 2013“ offers a good introduction to the use of Cyclictest. The presentation can be watched on Youtube. The PPT slides can be downloaded here.
Installation
git clone git://git.kernel.org/pub/scm/utils/rt-tests/rt-tests.git sudo apt-get install build-essential libnuma-dev cd rt-tests git checkout -b tmp tags/v1.0 make all
Cross compile
To install the Cyclictest on a MPC follow this guid.
Quickstart
sudo ./cyclictest -p 80 -t5
5 threads are created, which are called periodically. After a few minutes, the maximum latency can be roughly estimated.
Extensive Measurement
In order to benchmark the realtime performance of a system well appropriately, a measurement duration of at least 24h under real or artificial load is recommended. The frequency of different latencies can be counted and displayed in a histogram.
Start Benchmark
sudo ./cyclictest -Sp80 -l86400000 -i1000 -h1000 -q > histogramm.log
| -Sp80 | S = alle cores; p = priority-80 (Realtime) |
| -l86400000 | 86'400'000 cycles |
| -i1000 | 1000us per cycle |
| -h1000 | Latencies up to 1000us will be stored for the histogram |
| -q | quiet |
| Measurement time: | l86400000*i1000 = 86400e6us = 86400s = 24h |
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All measurements longer than -h1000 do not appear in the histogram. These measurements are counted and displayed at the end of the log file as Histogram Overflows:. The Maximum Latency is displayed as Max Latencies:.
To plot the histogram this Matlab script plotHistogramm.m can be used.
The homepage of OSADL explains well how such a histogram can be interpreted.