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7.
REAL-TIME LINUX
The definition of real-time is fuzzy, and depends a lot on the specific requirements of the customer
application. However, Linux is not a real-time operating system by any definition. Testing is the key to
determining if the standard Linux kernel meets your performance needs. If you experience problems
such as frequent FIFO overflows or system instability at high interrupt rates, this section provides tips on
possible solutions.
Diamond Systems has found that Linux is capable at driving most of our hardware at peak performance
so long as other resource intensive tasks are not running on the system. If your application performs well
in testing, you can skip to the next section.
7.1
Low interrupt latency kernel patches
The main problem with Linux real-time is that very high latencies (100ms or greater) can occur during
normal activity such as disk access or screen activity such as scrolling text on the console. A very widely
used solution to this to apply patches to the standard kernel which fix the parts of the kernel which are
causing these delays. There is no "best" one, so the customer must research the patches below to select
one or more which are ideal for their application. All of these solutions are available at no cost.
"Ingo Molnar's low-latency patch"
http://people.redhat.com/mingo/lowlatency-patches/
"Andrew Morton's scheduling latency patch"
http://www.zip.com.au/~akpm/linux/schedlat.html
MontaVista software's preemptible kernel patch"
http://www.linuxdevices.com/articles/AT4185744181.html
Additionally, the following article at O'Reilly on this subject is highly recommended
http://linux.oreillynet.com/pub/a/linux/2000/11/17/low_latency.html
7.2
FSM Labs Real-Time Microkernel
FSM Labs sells a unique solution for Linux real-time applications called RTLinux. This patented
technology is a microkernel which runs all of Linux as a thread which can be pre-empted when a realtime task needs to run, which results in excellent performance. It is available as both a distribution called
RTLinux and a patch to the standard Linux kernel. FSM Labs charges licensing and runtime feeds for
commercial use of this technology. Customers needing the very best real-time performance from Linux
and can to pay for it should consider this solution.
FSM Labs
http://www.fsmlabs.com/
 2002 Diamond Systems Corp.
Linux Development Kit User Manual v1.1
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