From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Pradeep" Subject: Re: Why is Linux not RTOS? Date: Thu, 5 Apr 2007 12:44:18 +0530 Message-ID: <024901c77752$06e6a170$59c8a8c0@SAGGITARIUS> References: <7783925d0704040521q3755394uf774884b5298eec2@mail.gmail.com> Mime-Version: 1.0 Content-Transfer-Encoding: 7bit Return-path: Sender: linux-newbie-owner@vger.kernel.org List-Id: Content-Type: text/plain; format="flowed"; charset="us-ascii"; reply-type="response" To: Rick Brown Cc: kernelnewbies , linux newbie > Hi, > > Why is Linux kernel considered a (hard) realtime OS? I already Linux kernel is never considered a real time OS. A real time OS should be predictable.The general linux kernel is not predictable because of many reasons. A few are it uses virtual memory. when there is virtual memory there will be page swaps which are un predictable. And the linux scheduler is not a deterministic one. There is a scheduler project which provides a deternistic behaviour to the scheduler.This scheduler is called O(1) scheduler. This gives a constant scheduling latency. This is used in many embedded linux to make it a real time OS. Ex: motavista > understand the basic reason is that the linux kernel does not > guarantee that a task will be completed on time. But I would > appreciate answers in terms of more of kernel jargons. > > What stops us from classifying kernel as hard RTOS? Is it because at An RTOS is just a facilitator to build Real time systems. A Real time system developer should analyse a RTOS wether is will be useful for his system. If some body is holding spin lock and making it non-preemptive its a bad design. So even a RTOS linux has spin locks. Its the designer who should take care. > times the kernel is non-preemptive (for e.g. while holding spinlocks)? > Has it got something to do with interrupt latency / scheduling latency > etc? > > Is the behaviour of the kernel (when it is preemptive) similar to hard > real time OS ?? > > Thanks, > > Rick > - > To unsubscribe from this list: send the line "unsubscribe linux-newbie" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.linux-learn.org/faqs - To unsubscribe from this list: send the line "unsubscribe linux-newbie" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.linux-learn.org/faqs