[ag-automation] hard rt ????

[Carsten Emde]

David,

> I have built the vanilla linux kernel 2.6.19 with the realtime patch (rt15)
> and was curious if it is now considered hard realtime?
We really do not differentiate between hard and soft realtime. Realtime 
compliance is like pregnancy - yes or not. There is no such thing as a 
bit pregnant nor is there a bit realtime. "Soft realtime" is important 
in the domain of marketing not engineering.

Yes, a vanilla Linux kernel patched with the realtime-preempt patch is 
considered "to have the potential to provide realtime performance". 
However, your system is not necessarily a realtime system. Your BIOS may 
have installed System Management Interrupts that will paralyze your 
system from time to time, some drivers may busy wait or some other 
mechanisms may counteract with the realtime-preempt patches.

This is why the realtime-preempt patches provide a large number of test 
tools. As an initial test, we would propose that you run cyclictest, e.g.

# cyclictest -t 3 -n -p 99

More details are given here:
http://www.osadl.org/Realtime-Preempt-Kernel.kernel-rt.0.html


Regards,

Carsten Emde.