Re: [2.4.17/18pre] VM and swap - it's really unusable

Daniel Phillips
2002-01-14T17:34:42Z

On January 14, 2002 02:45 pm, yodaiken@fsmlabs.com wrote:
> POSIX makes no specification of how scheduling classes interact - unless something changed
> in the new version.
>
> But more than that, the problem of preemption is much more complex when you have
> task that do not share the "goodness fade" with everything else. That is, given a
> set of SCHED_OTHER processes at time T0, it is reasonable to design the scheduler so
> that there is some D so that by time T0+D each process has become the highest priority
> and has received cpu up to either a complete time slice or a I/O block. Linux kind of
> has this property now, and I believe that making this more robust and easier to analyze
> is going to be an enormously important issue. However, once you add SCHED_FIFO in the
> current scheme, this becomes more complex. And with preempt, you cannot even offer the
> assurance that once a process gets the cpu it will make _any_ advance at all.

So the prediction here is that SCHED_FIFO + preempt can livelock some set of correctly
designed processes, is that it? I don't see exactly how that could happen, though that
may simply mean I didn't read closely enough.

--
Daniel