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    Subjectvoluntary-preemption: understanding latency trace
    I'm seeing a mismatch between my manually-measured timings and the
    timings I see in /proc/latency_trace.

    I've got a SCHED_FIFO kernel thread at the highest priority
    (MAX_USER_RT_PRIO-1) and it's sleeping on a wait queue. The wake is
    called from an ISR. Since this thread is the highest priority in the
    system, I expect it to run before the ISR threads and softIRQ threads

    In the ISR I sample sched_clock() just before the call to wake_up()
    and in the thread I sample sched_clock() again just after the call to
    sleep. I'm seeing an almost 4ms latency between the call to wake_up
    and the actual wakeup. However, in /proc/latency_trace, the worst
    latency I see during the running of this test is <500us.

    I must be misunderstanding how the latency traces are
    started/stopped. Can anyone shed some light? Thanks.

    My current setup is using -R5, running on a PII 400MHz system.

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      Last update: 2005-03-22 14:06    [W:0.017 / U:36.908 seconds]
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