Armin Steinhoff <armin@xxxxxxxxxxxx> writes: > Robert Schwebel wrote: >> On Tue, Sep 14, 2010 at 11:24:21AM +0200, Raz wrote: >>> anyone can say preempt rt is hard real time? >> Hard realtime has something to do with how you define "missing the >> deadline". If somebody cuts the cable of your roboter controller in the >> factory hall, the system misses the deadline. So it is all about >> probabilities: hard realtime systems have a very, very low probability >> of missing the deadline. However, in real life systems, it is> 0%. >> >> So yes, if you talk about real world, it is hard realtime. >> > Hm, and what do think about that statement from FSMLabs: > > "Linux “PREEMPT” real-time is a continuing experiment aimed at audio > and video playing with unreliable results and a detrimental affect on > “enterprise” performance" Kernel preemption is a complex thing. Letting the kernel be a low-priority realtime task (which is what most "enterprise" solutions do instead) still preempts the kernel, though only with realtime tasks, not competing tasks. Treating the kernel as a black box does not give you finer-grained control over device drivers etc unless you move the device drivers into the realtime realm. When a failure to service a device in a given time frame will result in hardware damage, you don't want a system as complex as the whole kernel involved. A realtime control system around that is more secure, but a dedicated, physically separate controller for meeting the hard constraints might be the safer choice. -- David Kastrup -- To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
