I mostly agree with you.
Mike Ji wrote:
Hi, folks,There are still several reasons 2.6 is not suitable for real-time applications:
I happen to read some white papers related to RTLinux. Below is some of my
personal thoughts.
* RTLinux's so called realtime extension-RTCORE **was* to address the previous issue--Linux is not realtime supported, for example, fully kernel-preemptive; posix realtime extension.
* After linux 2.6, I did not see any outstanding reason that people still
need to use a RTLinux **patch** to achieve realtime applications.
-scheduler latency is non deterministic ( time between interrupt firing and process execution waiting
on that interrupt). The rtirq patch helps by adding priorities to interrupts.
-Linux scheduler isn't real-time - only such schedulers such as EDF/RM will give you that.
-Data acquisition from disk is also non deterministic. This issue is much harder to deal with because its
almost impossible to bound the amount of time it takes read/write data, since you can't tell where the disk
arm is relative to how the data is placed on disk. Most real-time apps get around this simply by not writing
to disks.
-Caching hurts real-time application performance, in that running two real-time apps might cause the cache
to get continuously flushed (because the same cache lines are used), while running only one real-time app
might cause zero flushes. A solution is page coloring, but Linux 2.6 doesn't have this. There are patches, though.
* From os/kernel viewpoint, it is very hard for me to position RTCORE, but aSorry, I don't really know what you mean.
realtime patch. I mean, RTCORE is not able to be identified into any
well-known os architecture.
* If there is a very high performance micro-kernel, say, L4 or QNX/Neutrino, I personally think it is much better than the RTCORE stuff, which HAVE TO bind a secondary os as running time environment.
I agree the hierarchical approach isn't the correct model for a real-time system. Making Linux is deterministic is the
right solution, but implementing that is hard.
L4 is the Real-time operating system from the Research group in Germany, right? Doesn't it too require the use of a
micro kernel, such as fiasco or pistachio.
Has anyone played with the nucleus kernel from accelerated technology? If so, how did they like it?
More personal thoughts, Tim
Some personal thoughts,
-- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
-- Kernelnewbies: Help each other learn about the Linux kernel. Archive: http://mail.nl.linux.org/kernelnewbies/ FAQ: http://kernelnewbies.org/faq/
