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    SubjectRe: [patch] "HT scheduler", sched-2.5.63-B3
    On Thu, 6 Mar 2003, Jeff Garzik wrote:

    > Pardon the suggestion of a dumb hueristic, feel free to ignore me:
    > would it work to run-first processes that have modified their iopl()
    > level? i.e. "if you access hardware directly, we'll treat you specially
    > in the scheduler"?
    > An alternative is to encourage distros to set some sort of flag for
    > processes like the X server, when it is run. This sounds suspiciously
    > like the existing "renice X server" hack, but it could be something like
    > changing the X server from SCHED_OTHER to SCHED_HW_ACCESS instead.
    > Just throwing out some things, because I care about apps which access
    > hardware from userspace :)

    Well, close. But any low-latency access, even if somewhat buffered,
    is likely to be user visible if unresponsive. Clearly that means video
    memory like X and DRI, and sound, and mouse. If you define this generally
    it would include serial as well, probably not a bad thing.

    The proposal to backfeed priority from interractive processes to processes
    waking them sounds useful, perhaps that might be limited a bit however.
    Someone (Ingo?, Linus?) proposed limiting this to a fraction of the
    priority of the interractive process, but it might be more useful to
    simply limit how much could be added at one time, perhaps as a fraction of
    the delta between max and current interractive bonus, which would have the
    waker increase asymptomically toward max. Hysteresis is nice.

    I do agree that it would be better to identify processes using physical
    devices, far better than trying to identify some subset because it's

    I think this would include parallel port, although other than PL/IP I
    don't think of a case where it matters much.

    bill davidsen <>
    CTO, TMR Associates, Inc
    Doing interesting things with little computers since 1979.

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