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    SubjectRe: -rt more realtime scheduling issues
    On Fri, Oct 05, 2007 at 07:15:48PM -0700, Mike Kravetz wrote:
    > After applying the fix to try_to_wake_up() I was still seeing some large
    > latencies for realtime tasks.

    I've been looking for places in the code where reschedule IPIs should
    be sent in the case of 'overload' to redistribute RealTime tasks based
    on priority. However, an even more basic question to ask might be: Are
    the use of reschedule IPIs reliable enough for this purpose. In the
    code, there is the following comment:

    * this function sends a 'reschedule' IPI to another CPU.
    * it goes straight through and wastes no time serializing
    * anything. Worst case is that we lose a reschedule ...

    After a quick read of the code, it does appear that reschedule's can
    be lost if the the IPI is sent at just the right time in schedule
    processing. Can someone confirm this is actually the case?

    The issue I see is that the 'rt_overload' mechanism depends on reschedule
    IPIs for RealTime scheduling semantics. If this is not a reliable
    mechanism then this can lead to breakdowns in RealTime scheduling semantics.

    Are these accurate statements? I'll start working on a reliable delivery
    mechanism for RealTime scheduling. But, I just want to make sure that
    is really necessary.

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      Last update: 2007-10-08 20:47    [W:0.028 / U:4.540 seconds]
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