Messages in this thread | | | Date | Mon, 14 Jan 2002 06:45:48 -0700 | From | yodaiken@fsmlabs ... | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable |
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On Mon, Jan 14, 2002 at 02:17:46PM +0200, Momchil Velikov wrote: > >>>>> "yodaiken" == yodaiken <yodaiken@fsmlabs.com> writes: > yodaiken> It's not even clear how preempt is supposed to interact with SCHED_FIFO. > > How so ? The POSIX specification is not clear enough or it is not to be followed ?
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.
-- --------------------------------------------------------- Victor Yodaiken Finite State Machine Labs: The RTLinux Company. www.fsmlabs.com www.rtlinux.com
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