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DateMon, 28 Jul 1997 12:51:57 -0600 (CST)
FromAdam McKee <>
SubjectRE: [patch] QNX-style scheduling for Linux 2.0
Actually I did reverse the 0/31 priorities.  QNX has run-queue 31 as the
highest priority, run-queue 0 as the lowest.  I reversed this because it
doesn't affect performance/behaviour, and I found it a little nicer to
have run-queue 0 the highest priority.

Also, it is *not* possible for a process to get promoted beyond its base
priority unless root decides to re-nice it...  If a process's base
priority is too low, it can definitely starve...

It looks like VMS's scheduler and QNX's scheduler have a lot in common.  I
wonder who invented the adaptive scheduling technique?  It's quite simple
and effective.

	-- Adam


On Mon, 28 Jul 1997, Mark H. Wood wrote:

> On Sun, 27 Jul 1997, Adam McKee wrote:
> 
> > Hi there.
> > 
> > It does not do real-time in any way.  It only implements the QNX scheduler
> > as described by a couple of different sources.  I should probably make it
> > clear in the README that the patch does *not* do real-time, since the
> > "QNX" name might imply that it does real-time. 
> 
> OpenVMS has a scheduling scheme that is quite similar to QNX Adaptive, 
> except that (a) higher priorities are numerically greater, not less, and 
> (b) a process is never demoted past its base priority, which appears to 
> be possible in QNX.  VMS was supposed to be somewhat suitable for 
> realtime as well as general timesharing, so they rigged the scheduler to 
> always do strict round-robin scheduling within queues of priority 16 and 
> higher (that is, the highest-priority queues) with no time-slicing.  15 
> and below will move between queues, get pre-empted at quantum-end, etc.
> 
> Mark H. Wood, Lead System Programmer   MWOOD@INDYVAX.IUPUI.EDU
> Those who will not learn from history are doomed to reimplement it.
> 


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