Date: Wed, 4 Feb 1998 22:31:04 -0600 (CST) From: "Lee Crites (AEI)" <leec@adam.adonai.net> To: Jean-Marc Henriette <jeanmarc@starfleet.umd.edu> Cc: freebsd-questions@FreeBSD.ORG Subject: Re: Real time capability and FreeBSD Message-ID: <Pine.BSF.3.95.980204221705.9501C-100000@adam.adonai.net> In-Reply-To: <9802041315.ZM1492@starfleet.umd.edu>
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On Wed, 4 Feb 1998, Jean-Marc Henriette wrote: => I am a very happy home user of FreeBSD. Now, I'm trying to get my =>work place to accept it a bit more. Is there any plans to include some =>Real Time capability to FreeBSD, or should I not even bother? I know that =>Linux has a RT version of their stuff, but I don't want to have to learn =>how to manage a linux box when FreeBSD makes it so much easier.. My first question is what do you mean by "real time" capability? Here are some possible options: 1) you want data which is manipulated by one user to be seen right away by another user; 2) you want things happening now, as opposed to at some time in the future; 3) your processes depend upon data arriving in a deterministic way every time. The first two options are what some people call "soft" real-time. I've been able to manipulate/contort many versions of un*x, including FreeBSD into handling soft-real-time quite easily. Number three is where some of the purists will probably part ways with me. I can accept a hard-real-time definition which takes time constraints into consideration. The pure definition has nothing to do with time, only the arrival of data happening in a deterministic fashion -- and, of course, on time. I focus more on the "on-time" aspect. I figure if there is a, say, +/- 30% variance from the average, and I can handle the data arriving at 130% of the average, then I'm a happy guy. The fact that the system isn't exactly deterministic in nature, coupled with what many of the purists would call a totally unacceptable variance, don't cause me any grief. So (and this is why I have gone to the trouble of explaining the above), *I* find FreeBSD capable of handling my hard-real-time application as well. FreeBSD has the capability of manipulating the priority of a process so it can hog as much of the system as it needs, which is what I exploit. Your mileage will vary. This brings me to the second question: what is it you want to do? Or, put another way, what are your real needs? Armed with that tidbit of data, I might be able to help more. Lee
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