On Wed, 5 Mar 2003, Henry B. Hotz wrote:

> At 3:41 PM -0500 3/5/03, der Mouse wrote:
> >  > My understanding is that the problem affected most 68K Macs, and that
> >>  it was caused by the clock interrupt having the lowest priority
> >>  rather than (as would be usual) the highest.
> >
> >I have a IIci which suffers from _something_ of the sort.  When sitting
> >idle it keeps moderately good time, but put it under any sort of load
> >and it starts losing ticks like mad.
>
> No "something" about it.  That's the problem.  Time interrupts are
> blocked during any disk or Ethernet access.  MacOS works around the
> problem by rereading the RTC after every floppy access, and elsewhere
> as well probably.

Well, that's oversimplifying things slightly.  There are two problems,
which when combined, result in this issue.  The first is a poor priority
scheme.  The second is high latency interrupt handler routines.  Fix
either one, and you fix the problem.

Which reminds me, last time I tried to solve this problem, I was having
problems with panics when creating kernel threads during early boot.
Does anybody have any idea how to get around that?  I need a thread to be
marked as "ready to run" so that it can potentially be scheduled as soon
as interrupts are turned on.  Is there a right way to do that?


David

---------------------------------------------------------------------
David A. Gatwood                                dgatwood@gatwood.net
Developer Docs Writer                             dgatwood@apple.com
Apple Computer                                  dgatwood@mklinux.org

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