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    SubjectRe: voluntary-preemption: understanding latency trace
    On Thu, 2004-09-09 at 06:41, Kevin Hilman wrote:
    > 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
    > etc.
    > 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.

    Ingo, any ideas here? Looks like maybe the use of sched_clock is the


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