I've heard, that e.g. SpaceX use Linux on many of their flight computers. For instance, what hardware and what software tweeks are used to allow sampling of sensor data with a fixed frequency?
You can use Linux with the Preempt RT patch or Xenomai, which is using a kind of micro kernel in addition to the Linux Kernel. The downside is you have to rewrite your drivers for Xenomai.<p>I thought that the latter was better in terms of performance but the article below seems to affirm they are not that big. (but it is coming from the Preempt RT side)<p><a href="http://linuxgizmos.com/real-time-linux-explained/" rel="nofollow">http://linuxgizmos.com/real-time-linux-explained/</a>
The basic tweak is overprovisioning. If the computer is not busy it will get tasks done on time and not freeze up. If it has too much work to do in a time frame than it is not going to get it all done. The one thing it can really do differently is abort a task early when it is clear that that task can't be done on time, but then you will get complaints from the people whose tasks are responsible from that task completing.
for PCs you can try the jitter measurement from linuxcnc <a href="http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Latency-Test" rel="nofollow">http://wiki.linuxcnc.org/cgi-bin/wiki.pl?Latency-Test</a>