[477] in linux-announce channel archive
POSIX.4_scheduler
daemon@ATHENA.MIT.EDU (Lars Wirzenius)
Wed Apr 19 13:09:45 1995
Date: Wed, 19 Apr 1995 17:02:26 +0300
From: Lars Wirzenius <wirzeniu@cc.helsinki.fi>
To: linux-activists@niksula.hut.fi, linux-announce@vger.rutgers.edu
X-Mn-Key: announce
From: dave@ee.rochester.edu (David F. Carlson)
Newsgroups: comp.os.linux.announce
Subject: POSIX.4_scheduler
Organization: University of Rochester, School of Engineering
Keywords: Posix.4, scheduler, Linux, kernel
Approved: linux-announce@news.ornl.gov (Lars Wirzenius)
Followup-to: comp.os.linux.development.system
*******************************************************************************
**
** Copyright 1995 David F. Carlson (carlson@dot4.com)
** Copyright 1995 Dot4, Inc.
** All rights reserved
**
** POSIX 1003.1b Process Scheduler (POSIX.4)
** Provided to the Linux Community by Dot4, Inc.
**
** Dot4 is a provider of professional services for POSIX-based
** real-time systems from embedded to distributed.
**
** For more information call:
**
** Dot4, Inc. (800) 834-1951 ** email: dot4@dot4.com
** The Real-Time Specialists
**
*******************************************************************************
This is a POSIX.4 compliant real-time scheduler for our favorite free OS!
Theory:
Other than adding the required system calls, the trick is that whenever a
process is made runnable, and it is a POSIX scheduled process, it tickles
a mask of run bits, and sets the need_resched flag. At the next opportunity,
(ie., clock interrupt, end of system call, etc.) the scheduler finds the
highest priority runnable process -- and runs it.
Layout:
The libc contains the system call pieces. Archive these into /lib and /usr/
lib/gcc-lib/linux... etc.
The "test" directory contains a nice-like program. See the usage message
for help. All of the fields are optional. Just a pid will print the
scheduling domain of the target. Useful as there is no other way to detect
a POSIX scheduled process.
The linux directory contains kernel/psched.c and include/linux/psched.h and
the dot4.patch. CP these to your kernel build area. Apply the patch to
linux.1.2.0 (or equivalant).
Limitations:
The RR quantum is compile-time fixed. It will be made runtime modifiable
per process controlled RSN. The RR domain has had too little debug.
Notes:
Use the vt consoles at first. Remember XWindows uses several timeshare
processes to make your shell echo to you! Log a max priority vt in before
you play. (Console switching is at interrupt priority -- it works even if
the a FIFO scheduled process is in an infinite loop.) Console switching to
XWindows is *NOT* interrupt driven -- and then you may be stuck.
TBD: Manpages for the system calls and rtnice. A hacked /proc and ps to
show the RT processes.
Practical Consideration:
Don't put a SCHED_FIFO process into an infinite loop.
The ftp site is sunsite.unc.edu:/pub/Linux/Incoming.
Good luck.
dfc
carlson@dot4.com
Dot4, Inc. The Real-Time Specialists
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