RE: [patch] QNX-style scheduling for Linux 2.0

Mark H. Wood (mwood@mhw.OIT.IUPUI.EDU)
Mon, 28 Jul 1997 08:49:27 -0500 (EST)

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.