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    SubjectRe: PREEMPT_RT vs ADEOS: the numbers, part 1

    * Karim Yaghmour <karim@opersys.com> wrote:

    > Ingo Molnar wrote:
    > > ok, this method should work fine. I suspect you increased the parport
    > > IRQ's priority to the maximum on the PREEMPT_RT kernel, correct? Was
    > > there any userspace thread on the target system (receiving the parport
    > > request and sending the reply), or was it all done in a kernelspace
    > > parport driver?
    >
    > This is all done in kernelspace. I'll check with Kristian for the
    > rest. In the mean time, let me know if you have any recommendations
    > based on the fact that it's indeed in the kernel.

    if you want to measure hw-interrupt delays then under PREEMPT_RT you'll
    need to use an SA_NODELAY interrupt handler. (which is a PREEMPT_RT
    specific flag) If you use normal request_irq() or some parport driver
    then the driver function will run in an interrupt thread and what you
    are measuring is not interrupt latency but rescheduling latency.

    Ingo
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