Comparing VXworks to RTLinux

A couple of years ago, one of our salesmen asked us to comment on a comparison between VxWorks and RTLinux performance that had a prospective customer worried. When we tracked down the article, we were dumbfounded that it was being taken seriously. The article was a student paper from a mid-level class in Networks with some obvious limitations that I’m sure are known to the author. (I am very thankful my undergraduate student papers were written before the Internet so they don’t show up years later.) The paper compares the old RTLinuxFree 3.1 to VxWorks. Here are some curiosities.

  • The author writes:
    “We configured both RTOSes to use round-robin scheduling policy to determine context switch time.” That’s impressive given that RTLinuxFree 3 did not ever support round-robin scheduling.
  • Measurements show RTLinux with better priority inheritance performance! RTLinux has never implemented priority inheritance for reasons described in my paper Priority Inheritance: Hack or Error.
  • There is a comparison of interrupt latency on an MPC8260 that is dubious: we measured RTLinux 3.x with about 1/10 of the latency he shows.
  • He compares the performance of a message receive call, despite the absence of such a call from RTLinux 3.1.
  • and so on …

The paper is available on a server in Korea and it shows up near the top of searches. There is a reason we don’t do that comparison (VxWorks license), but there is no good reason that project teams seriously considering options can’t do the comparison for themselves.

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