From mboxrd@z Thu Jan 1 00:00:00 1970 Message-ID: <3843ED00.20D47DF4@netx4.com> Date: Tue, 30 Nov 1999 10:28:00 -0500 From: Dan Malek MIME-Version: 1.0 To: Graham Stoney CC: linuxppc-embedded@lists.linuxppc.org Subject: Re: Real Time response/latency question References: <19991130034844.1B3E0F380@elph.research.canon.com.au> Content-Type: text/plain; charset=us-ascii Sender: owner-linuxppc-embedded@lists.linuxppc.org List-Id: Graham Stoney wrote: > > Hi folks, > > I'm looking at software architecture questions, and wondering how much > application domain work I can move out of driver land and into user space, I believe this is a good programming practice, and in many cases I don't even write a driver when the application is allowed to run with root privilege. > .... Can anyone give me a rough idea of the maximum > latency in user space I could expect on an 860T based system with multiple > threads, where only one thread has SCHED_RR realtime scheduling priority? You can't answer this question due to the design and implementation of the kernel. Most "real-time" systems can't either once you throw protocol stacks, file systems, disk drives, and other external devices or distributed services into the feature mix. I have successfully written applications that required sub-millisecond latency. You just have to be careful about other applications in the system, and remember that you can't preempt the kernel. If you have hard real-time requirements, check into the RT-Linux features. These are starting to mature, and can make scheduling guarantees within the confined real-time domain. -- Dan ** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/