Sven Erdem
29 April 2021
For many developers, QNX is the operating system of choice, when it comes to developing on embedded systems. However, the performance limits are exceeded quickly, especially if you're working on low-end hardware. As a result, you'll likely need to perform an investigation to find the bottlenecks that contribute to reaching these limits, in order to configure your application to fit the requirements of your system.
There are many reasons why an application might be slow. Any number of bottlenecks could be causing the delays. In our experience, file reads and writes have been relevant factors, due to bandwidth limitations.
To speed up the investigation process, KDAB created a script which lets us dig for specific system calls and provides us with visual information about their occurrences. According to our findings, on QNX, you can gather information about system calls with the command fsysinfo.
Recording the output of fsysinfo to a file gives a database for our script. Specify the time period between adjacent samples, in milliseconds. Wait an appropriate amount of time, then exit fsysinfo by killing it (or hit CTRL+C when executed from a terminal).
# Tip: you can clear all values before recording with following command
$ fsysinfo -Z DEVICE|FILESYSTEM
# Record samples
$ fsysinfo -l PERIOD DEVICE|FILESYSTEM > OUTPUTFILEFor more information on the fsysinfo command, please see http://www.qnx.com/developers/docs/7.1/#com.qnx.doc.neutrino.utilities/topic/f/fsysinfo.html.
Then, a decision of what shall be plotted must be made. This is done with arguments to our script.
$ fsysinfo_plot.py [OPTION]... FILE -- KEY...Here are a few examples:
The first example plots the amount of bytes read and written to the disk, using a logarithmic scale. It calculates the difference between two points in time (samples) and gives a visual representation of when and how many bytes have been read and written. Also the legend is moved to the top right corner. Note that the x-axis corresponds to the previously recorded samples and the specified preriod is the inverse of samples per second (1 / period).
$ fsysinfo_plot.py --diff --log --legendright fsysinfo_rwdata_log -- "DISK I/O.read.bytes" "DISK I/O.write.bytes"The next example presents the occurrences of 4 system calls and relates the corresponding amount by stacking them on top of each other.
$ fsysinfo_plot.py --stackplot fsysinfo_rwdata_log -- SYSCALL.create SYSCALL.delete SYSCALL.open SYSCALL.statTo find out more about how and what to plot, use the help argument:
$ fsysinfo_plot.py --help
this script plots a qnx fsysinfo log
usage
fsysinfo_plot.py [OPTION]... FILE -- KEY...
whereas the key determines what shall be printed
the keys are formatted like so: "SYSCALL.rename"
example
fsysinfo_plot.py --diff my_fsysinfo_log -- SYSCALL.open "DISK I/O.read" "DISK I/O.write"
options
--stackplot performs a stackplot instead of a usual one
--diff calculates the difference between 2 samples
--avg N averages between N samples (applied after diff)
--log logarithmic scale (be careful with negative values or when using diff)
--legendright display legend on the top right instead of top left corner
keys
DISK I/O read, r/a, write, io req, direct, bad, read.bytes, r/a.bytes, write.bytes, io req.bytes, direct.bytes
CACHE read, write, mfu, mru, ratio, read.bytes, write.bytes
SYSCALL open, create, delete, trunc, stat, namei, modes, owner, rename, devctl, sync, pause, change, timed, write, read, write.bytes, read.bytes
NAMES exist, enoent, misses, unsuit, stale, rate
BMAP hit, miss, rate
VNODES create, hit, rate, lock, recycl
SLAB map, unmap, active
THREADS create, destro, pool
recording a log is possible with `fsysinfo -l PERIOD DEVICE|FILESYSTEM > OUTPUTFILE`
whereas PERIOD is in milliseconds
please look into the fsysinfo manual for more informationPlease make sure to have the following dependencies installed:
You can find the script here: https://github.com/KDAB/qnxtools/blob/main/fsysinfo_plot.py
About KDAB
The KDAB Group is a globally recognized provider for software consulting, development and training, specializing in embedded devices and complex cross-platform desktop applications. In addition to being leading experts in Qt, C++ and 3D technologies for over two decades, KDAB provides deep expertise across the stack, including Linux, Rust and modern UI frameworks. With 100+ employees from 20 countries and offices in Sweden, Germany, USA, France and UK, we serve clients around the world.
Choose between learning advanced QML programming, Modern C++, integrating Rust and Qt or 3d rendering with Vulkan. The KDAB Training Day 2025 will take place in Munich on the 8th of May, right after the Qt World Summit on 6th to 7th of May.
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