Re: scheduler (sched_4bsd) questions

From: Stephan Uphoff (ups_at_tree.com)
Date: 09/19/04

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    To: John Baldwin <jhb@FreeBSD.org>
Date: Sat, 18 Sep 2004 19:08:34 -0400

    On Sat, 2004-09-18 at 16:53, John Baldwin wrote:
    > On Saturday 18 September 2004 01:42 pm, Stephan Uphoff wrote:
    > > On Fri, 2004-09-17 at 21:20, Julian Elischer wrote:
    > > > Stephan Uphoff wrote:
    > > > >If this is true kernel threads can be preempted while holding
    > > > >for example the root vnode lock (or other important kernel
    > > > >resources) while not getting a chance to run until there are no more
    > > > >user processes with better priority.
    > > >
    > > > This is also true, though it is a slightly more complicated thing than
    > > > that.
    > > > Preempting threads are usually interrupt threads and are thus usually
    > > > short lived,.
    > >
    > > But interrupt threads often wake up other threads ...
    >
    > That are lower priority and thus won't be preempted to. Instead, they run
    > when the interrupt thread goes back to sleep after it finishes.

    Lower priority than the interrupt threads.
    They can however have a priority better than the interrupted thread
    holding the kernel resource.
    In this case the newly awoken threads will be next to run.
    If they are compute bound in user space or wake other threads with
    better priorities it might take a while until the system switches back
    to the interrupted thread.

            Stephan

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