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    SubjectRe: Good performance (hard realtime ??) on 2.6.16 patched with patch-2.6.16-rt29 from Ingo Molnar
    Date
    Felix Oxley writes: 

    > Could you explain to me, in nice easy steps, how you got the measurement?
    1) for details see: http://tapas.affenbande.org/?page_id=6.

    2) Sending box and sending process
    * periodically sends udp message using broadcast adress 192.168.2.255
    * this process at RT priority FIFO (using chrt tool)
    * put IRQ of network card to RT 99 FIFO prio
    * box is idle (to create sort of 'stable') reference timing

    3) receiving box
    * blocking read on udp socket
    * put to RT FIFO 99 (chrt tool)
    * process cannot be swapped out (mlockall call)
    * while [1] do make -j100 && make clean; done;
    * put softiqr-net-rx to RT FIFO 99 (using chrt)
    * watchdog/0 not RT (i'm not sure this is mandatory)
    * put IRQ of network card to RT FIFO prio 99
    * Time measurement the cpu clock using gettimeofday calls

    > Specifically what triggered the 'start' of your time slice?
    on sending box: usleep with 20000 interval (20 millisecond)
    on receiving box: blocking read on udp socket

    > BTW, where you using hi resolution timers?
    No, only usleep (maye it uses highres timers in the libs/kernel)

    > You say the max latency was 512usecs. What were the mean and mode?
    Not measured...

    > (Regarding Hard Real Time, my understanding is that that depends on a
    > _guarantee_ that the system will always be able to produce the 'result'
    > within the required interval. Ingo's -rt patches may give exceedingly
    > good responsiveness but they offer no guarantees, so they cannot be
    > considered Hard Real Time)
    Correct. In my case the repsonsiveness is acceptable in a real time control
    system where sporadic deadline misses are acceptable.

    Thanks
    Carl.

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