home *** CD-ROM | disk | FTP | other *** search
- Path: sparky!uunet!zaphod.mps.ohio-state.edu!wupost!darwin.sura.net!spool.mu.edu!olivea!hal.com!darkstar.UCSC.EDU!osr
- From: welch@parc.xerox.com (Brent Welch)
- Newsgroups: comp.os.research
- Subject: Re: Microkernel for Real-Time Computing
- Message-ID: <1egg77INNi7h@darkstar.UCSC.EDU>
- Date: 19 Nov 92 16:43:19 GMT
- References: <1e92s7INN8dg@darkstar.UCSC.EDU>
- Organization: Xerox PARC
- Lines: 39
- Approved: comp-os-research@ftp.cse.ucsc.edu
- NNTP-Posting-Host: ftp.cse.ucsc.edu
- Originator: osr@ftp
-
- yk7m@uvacs.cs.Virginia.EDU (Young-Kuk Kim) writes:
-
- >Does anybody explain to me why and how a microkernel (e.g., Mach, Chorus)
- >can provide a deterministic computing base for real-time applications,
- >while a traditional monolithic kernel cannot?
-
- >In other words, my questions are:
-
- >1. What are the advantages of microkernel for real-time applications
- >over a traditional monolithic kernel, and why?
-
- >2. What are the advantages of microkernel approach, comparing to
- >traditional real-time executives?
-
-
- >-- Young-kuk Kim
-
- Operating system structure and real time scheduling ought to be
- orthogonal issues. In fact, for example, most versions of Mach
- that you'll find in use are not real-time kernels. For the source
- of truth on that, send mail to tokuda@cs.cmu.edu and ask him
- what the state of real-time mach is.
-
- The key to real time is in the scheduler, and whether or not
- a process is pre-emptable when it is executing inside the
- protected operating system kernel. The latest version of SunOS
- (Solaris 2.0), for example, has preemptible kernel threads.
- Most versions of UNIX however, do not allow a process to be
- interrupted when it is executing inside the kernel (not counting
- device interrupts). Another important consideration is how long
- it takes to service device interrupts. Interrupts and pre-emption
- usually have to be blocked when servicing the interrupt. However
- you don't want to do full blown TCP protocol handling at this point.
- Instead, you have to structure your system so that a thread is
- scheduled to do most of the work, even if it is a kernel thread.
-
- --
-
- Brent Welch
-