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SubjectRe: Prioritized I/O
Steven Suson writes:
> I've been thinking about the discussions on latency, especially in
> regards to multilmedia recording, etc. If I/O were prioritized in the
> way that CPU utilization is, then this would allow R/T processes to also
> take precendence for I/O, thus reducing latency. In addition, this
> yields all sorts of benefits for time sensitive I/O.
> Any thoughts? Opinions? Etc.?

I prototyped something like this in SunOS years ago. It was a big win
for responsiveness because I used it to make executable pagefaults have
higher priority than writes.

It never went in because there are fairness issues - consider a system
generating a lot of dirty pages and you are giving reads higher priority.
The system grinds to a halt. I never solved that part of the problem.

Anyway, there is an easy way to do this - every operating system has a
disk queue with pending disk I/Os. Just turn that into multiple queues.

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