Path: utzoo!utgpu!jarvis.csri.toronto.edu!rutgers!tut.cis.ohio-state.edu!ucbvax!CS.PURDUE.EDU!comer
From: comer@CS.PURDUE.EDU (Douglas Comer)
Newsgroups: comp.os.xinu
Subject: Re:  Process quantum
Message-ID: <8906122123.AA23467@merlin.cs.purdue.edu>
Date: 12 Jun 89 21:23:57 GMT
Sender: daemon@ucbvax.BERKELEY.EDU
Organization: The Internet
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Guilbot-Martin,

   If I understand your letter, it basically raises the question of why
system calls other than time-slicing can cause context switching.  The
answer is that the Xinu priority scheme allows any process that becomes
ready to gain the CPU provided that no higher priority process is executing.
This makes sense in most applications and is *necessary* in a real-time
environment.  One possible modification is to keep with each process a
value that represents "remaining time in timeslice".  The value would be
saved when the process loses control of the CPU and restored when the
process regains control.  In considering this alternative, I decided
that the slight improvement in precision did not justify the accompanying
increase in overhead.

Doug