Red Hat has selected FSMLabs' RTLinux as its standard approach to hard real-time Linux application requirements, according to a joint press release issued today. FSMLabs CEO Victor Yodaiken explained that the two companies have signed a memorandum of understanding covering cross-promotion, resale, and joint development. “This partnership allows both FSMLabs and Red Hat to focus on [their respective] core strengths while still giving customers a total package,” said Yodaiken.

RTLinux is based on a patented technology, whereby a hard real-time kernel runs concurrently with (and enhances) a general purpose operating system (OS) such as Linux. Through this dual-kernel (RTLinux + Linux) architecture, time-critical “real-time” tasks are serviced by the real-time kernel (RTLinux) with negligible interference from the routine system functions performed by the general purpose OS (Linux). The approach allows Linux-based systems to be used in real-time applications such as machine control, multimedia servers, and high speed telecommunications.

An alternative to the dual-kernel real-time Linux approach, which consists of incorporating real-time functionality directly into the Linux kernel by means of various extensions and patches, has been strongly promoted by several Embedded Linux companies including MontaVista Software, TimeSys, and REDSonic. MontaVista, in particular, has developed open source modifications to the Linux kernel's task scheduling and preemptability, resulting in what MontaVista claims are substantial improvements to the inherent real-time performance of Linux. TimeSys has added what it calls “quality of service” enhancements. Since there has been considerable ongoing controversy over which approach is superior, Red Hat's endorsement of the dual-kernel RTLinux approach is certain to spark a lively renewed debate.

Commenting on the approach of building real-time capability directly into the Linux kernel, Alan Cox (one of the two most prominent developers of the Linux kernel and a Red Hat employee) explained that “Red Hat felt that attempting to retrofit full real-time throughout a general purpose OS [would result in] a poor general purpose OS with poor real-time support.” “The beauty of RTLinux is that it gives us top-class hard real-time with only tiny modifications to the Linux kernel and almost no measurable performance impact,” Cox added.

“MontaVista is barking up the wrong tree with its idea of trying to sprinkle real-time throughout the Linux kernel,” added Michael Tiemann, Red Hat's CTO. “The Linux 2.4 kernel with the 'low latency' enhancements developed by Ingo Molnar provides latencies on the order of one or two milliseconds, which is sufficient for meeting the most important response-time requirements of Linux, which are generally on the order of 16 milliseconds (corresponding to 60 frames/sec),” Tiemann said. “When lower latencies than that are needed, adding RTLinux can provide worst-case interrupt latencies on the order of 10-20 microseconds.”

 
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