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    SubjectRe: [patch, 2.6.11-rc2] sched: RLIMIT_RT_CPU_RATIO feature

    * Ingo Molnar <mingo@elte.hu> wrote:

    > negative nice levels are a guaranteed way to monopolize the CPU.
    > SCHED_FIFO with throttling could at most be used to 'steal' CPU time
    > up to the threshold. Also, if a task 'runs away' in SCHED_FIFO mode it
    > will be efficiently throttled. While if it 'runs away' in nice--20
    > mode, it will take away 95+% of the CPU time quite agressively.
    > Furthermore, more nice--20 tasks will do much more damage (try thunk.c
    > at nice--20!), while more throttled SCHED_FIFO tasks only do damage to
    > their own class - the guaranteed share of SCHED_OTHER tasks (and
    > privileged RT tasks) is not affected.

    furthermore, the current way of throttling SCHED_FIFO tasks that violate
    the limit makes it less likely that application writers would abuse the
    feature with CPU-intensive apps, because _if_ you violate the limit then
    the penalty is high. E.g. a blatant violation of the limit via a pure
    CPU loop ends up getting much less CPU time than even the limit would
    allow for. For audio/RT apps this is fine, because they must plan their
    CPU overhead anyway so they are a much more controlled environment and
    just do things properly to avoid the penalty.

    Ingo
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