Hi list, I have asked this before, but some of my doubts remain. So I want to know that when it comes down to code, what stops the plain linux kernel from being called RTOS? Please note that I understand that there are different Linux based patches / projects that make LInux realtime, but I want to know about the kernel from kernel.org - what makes it a non-RTOS? As far as I could understand, it is dues to two factors: 1) Its use of virtual memory (because the user pages may be paged out thus causing unpredictable delays). But what if given that the user applications always call the "mlockall()" to lock all the pages in memory? Is this reason then taken care of? Also , do all RTOSes do not make use of virtual memory? 2) No specified worst case latency (which is the definition of RTOS). I could find that there are two kinds of latencies: a) Scheduling latency: Well, with the latest 2.6 kernel and with Ingo Molner's O(1) scheduler, isn't this now deterministic? b) Interrupt latency: This seems to be the main cause for which kernel cannot be called RTOS< because a driver may hold spinlocks / disable preemption for any amount of time? Finally, what I could conclude from the googling was that the only bottleneck with linux is that certain areas of code are non-preemptible (where spinlocks are held or where interrupts are disabled). If some how we could make entire kernel preemptible, then it would be an RTOS. Is this right? Lastly, isn't scheduling latency and interrupt latency contradictory? I mean there will always be a tradeoff between the two. Any efforts to decrease on / make it predictable will increase / make unpredictable of the other. No? Thanks, Rick -- To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs
