Messages in this thread | | | Date | Mon, 14 Jan 2002 15:46:40 -0700 | From | yodaiken@fsmlabs ... | Subject | Re: [2.4.17/18pre] VM and swap - it's really unusable |
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On Tue, Jan 15, 2002 at 12:34:01AM +0200, Momchil Velikov wrote: > One can consider a non-preemptible kernel as a special kind of > priority inversion, preemptible kernel will eliminate _that_ case of > priority inversion.
The problem here is that priority means something very different in a time-shared system than in a hard real-time system. And even in real-time systems, as Walpole and colleagues have pointed out, priority doesn't really capture much of what is needed for good scheduling.
In a general purpose system, priorities are dynamic and "fair". The priority of even the lowliest process increases while it waits for time. In a raw real-time system, the low priority process can sit forever and should wait until no higher priority thread needs the processor. So it's absurd to talk of priority inversion in a non RT system. When a low priority process is delaying a higher priority task for reasons of fairness, increased throughput, or any other valid objective, that is not a scheduling error.
> > Regards, > -velco
-- --------------------------------------------------------- Victor Yodaiken Finite State Machine Labs: The RTLinux Company. www.fsmlabs.com www.rtlinux.com
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