Just a few thoughts ... It is not possible to have a fully deterministic real-time operating system on a processor that uses instruction/data caches. ie you have to turn off the cacheing to achieve determinism and eliminate performance jitter (which then degrades the average performance).
>From what I understand PREEMPT_RT does not really improve the real-time performance of linux if you stick to user level applications. You have to start doing things at kernel level, which can get difficult and break many of the existing device drivers. Anyway, who said all embedded applications require a deterministic real-time performance? Soft real-time performance is generally good enough for a lot of applications. For real-time, the PRU co-processors are the way to go. There are a number of papers around on the web comparing the performance of normal linux, PREEMPT_RT and Xemonai in real-world situations (use google to find them). They make for interesting reading and caused me to re-access my approach to embedded linux systems. Regards ... On Friday, February 21, 2014 7:20:39 PM UTC+11, [email protected] wrote: > > I am trying to figure out how to create a kernel for the BBB that supports > PREEMPT_RT. It's kind of strange that the BBB's default kernel does not > even have PREEMPT activated. Such a board doesn't fit to many embedded > applications where we need at least some kind of determinism. It is even > worse, that nobody seems to care about this problem. Contrary to that, the > Raspberry PI's standard kernel has PREEMPT activacted from the very > beginning. > > I have tested Robert Nelsons kernel 3.8.13-r9 ( > https://github.com/beagleboard/kernel/tree/3.8-rt). It does not have > PREEMPT_RT activated by default. When doing so, it does not boot. But > activating PREEMPT does work. However, development of this branch has > stopped several months ago. The official source for RT Linux (3.8.13) has > evolved since then. Meanwhile there's an rt17 patch set ( > https://www.kernel.org/pub/linux/kernel/projects/rt/3.8/). Did anybody > give this a try? Does it work with the BBB? > > > -- For more options, visit http://beagleboard.org/discuss --- You received this message because you are subscribed to the Google Groups "BeagleBoard" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/groups/opt_out.
