On Mon, 2008-03-03 at 13:51 +1300, Michael van der Gulik wrote:
On Mon, Mar 3, 2008 at 2:01 PM, Robert F. Scheer rfscheer@speakeasy.net wrote: Also, after installing the linux-rt ("realtime") kernel from Ubuntu repositories, the delay bag performance was horrible, as mentioned earlier, but not in the same league of hurt as the results you've just posted.
I can't tell if there's just the one real-time Linux which has multiple names or if they're separate projects; I'm seeing linux-rt, Linux/RT, rtlinux, RT-Linux, ...
The version in the Ubuntu repository is really a low-latency kernel based on work by Thomas Gleixner and Ingo Molnar. It is basically the standard Ubuntu kernel with their patch tailored for some Ubuntu differences.
It is intended to support automation, robotics, telco and multimedia authoring for example.
Supposedly, it adds support for high resolution timers and full preemption. (I haven't had time to get into what that really means or requires, sorry).
It is not a real "real-time" Linux kernel by any means. It was an easy experiment that I did but not a very serious one.
- Robert
Anyway, if they're all the same thing, then you're not using any of the real-time features:
http://www.faqs.org/docs/Linux-HOWTO/RTLinux-HOWTO.html
In order to get real-time performance, it sounds like you need to write your real-time code as a kernel module, and the rest of your application (the parts that don't need to be real-time) would run in user-land and communicate using a real-time FIFO character device.
Also, by real-time, they really do mean real-time: "Worst case interrupt latency on a 486/33Mhz PC measures well under 30 microseconds, close to the hardware limit." (ref: http://www.linuxdevices.com/articles/AT3694406595.html, assuming it's the same RT-Linux).
Gulik.
-- http://people.squeakfoundation.org/person/mikevdg http://gulik.pbwiki.com/