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    SubjectRe: [PATCH 5/6] sched: SCHED_FIFO/SCHED_RR watchdog timer
    On Wed, Oct 31, 2007 at 11:03:28PM +0100, Peter Zijlstra wrote:
    > On Wed, 2007-10-31 at 22:49 +0100, Andi Kleen wrote:
    > > Peter Zijlstra <> writes:
    > >
    > > > Introduce a new rlimit that allows the user to set a runtime timeout
    > > > on real-time tasks. Once this limit is exceeded the task will receive
    > > > SIGXCPU.
    > >
    > > Nice idea.
    > >
    > > It would be even nicer if you could allow a couple of them. Partition
    > > the RT priorities into a few classes and have an own limit for each them.
    > >
    > > A small number of classes (3-4) would be probably enough and not bloat
    > > the rlimits too much.
    > >
    > > I'm thinking of the case where you have different kinds of real
    > > time processes. Like your mp3 player which you want to be slightly
    > > real time, but with a low SIGXCPU limit.
    > >
    > > And then something else real time which is more important and
    > > you would set a higher limit. etc.
    > But its an rlimit, it can be set per process. Not sure what multiple

    That's impractical -- you would need to patch the process or call
    it from a special program, which is not nice.

    rlimits are useful to set a limit during log in. For that the
    children can be all kinds of different processes and possibly use
    different settings.

    > classes per process would gain us, let alone how that process has to
    > figure out which class to use.

    You set the classes once per rlimit (e.g. in a pam module)
    Then the processes set different scheduling priorities by themselves
    (standard programs do that). Then that priority would map to a different


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