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From: dstewart@fas.ri.cmu.edu (David B Stewart)
Newsgroups: comp.unix.wizards
Subject: Re: What new system calls do you want in BSD?
Message-ID: <7904@pt.cs.cmu.edu>
Date: 9 Feb 90 05:01:15 GMT
References: <11102@encore.Encore.COM>
Distribution: usa
Organization: Carnegie-Mellon University, CS/RI
Lines: 30

Another feature that would be useful as a BSD system call is to
lock down one or more pages in physical memory, and allow other
processors on a common backplane to mmap it.  Of course, this assumes
appropriate hardware architecture.

As an example, suppose one CPU is running BSD UNIX, while all others have
some kind of Real-Time OS (our current situation, except we have SunOS). 
It is possible for the UNIX machine to mmap part of the other CPUs
memory; but the reverse is not possible.  The Real-time CPU cannot
mmap part of the BSD UNIX memory.  Such communication can greatly
increase the speed of communication between the Real-Time and Non-real-time
environments.  On the Sun, this is possible using DVMA (Direct Virtual
Memory Access), but it is rather awkward to use.  The space reserved
for DVMA is available to only kernel routines.  User routines do
not have access to that memory.  Replacing this functionality with
a system call would allow user processes to access the reserved memory
on the UNIX system, while at the same time letting other CPUs on the
backplane also access the memory.  

I really have no clue if the above type of system call is feasable
to implement in BSD, since I am not familiar with the internals of 
BSD.  Any futher insight is welcome.

~dave

-- 
David B. Stewart, Dept. of Elec. & Comp. Engr., and The Robotics Institute, 
	Carnegie Mellon University,  email: stewart@faraday.ece.cmu.edu 
The following software is now available; ask me for details
        CHIMERA II, A Real-time OS for Sensor-Based Control Applications