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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.12-V0.7.49-00


    On Wed, 22 Jun 2005, Esben Nielsen wrote:

    >
    > On Tue, 21 Jun 2005, Ingo Molnar wrote:
    >
    > >
    > > * Esben Nielsen <simlo@phys.au.dk> wrote:
    > >
    > > > I am seeing very high latencies on 2.6.12-RT-V0.7.50-04 with a
    > > > modified realfeel2: maximum is 246 us. Shouldn't it be in the order of
    > > > 50 us?
    > >
    > > i never got reliable results from realfeel - it should do the kind of
    > > careful things rtc_wakeup does to avoid false positives.
    > >
    > I tried with rtc_wakeup while I was at work (which is on my disk at home)
    > - but it crashed my machine (one have to be _very_ carefull about what you
    > do when you run in a task with RT priority!). I have fixed it now (see
    > below patch) and it is running for the night. Let us see if I get similar
    > results.
    >

    Yep, just as I pressed sent before I saw the following:

    ./rtc_wakeup -n 1000000
    rtc_wakeup - press ctrl-c to stop - use -h to get help
    freq: 1024
    max # of irqs: 1000000
    jitter threshold: 5% (48 usec)
    output filename: /dev/null
    rt priority: 80(90)
    aquiring rt privs
    getting cpu speed
    696948901.455 Hz (696.949 MHz)
    # of cycles for "perfect" period: 680614 (976 usec)
    setting up ringbuffer
    setting up consumer thread
    setting up /dev/rtc
    locking memory
    turning irq on
    new max. jitter: 0.2% (1 usec)
    new max. jitter: 0.5% (4 usec)
    new max. jitter: 0.6% (5 usec)
    new max. jitter: 0.7% (6 usec)
    new max. jitter: 1.0% (9 usec)
    new max. jitter: 1.7% (16 usec)
    new max. jitter: 1.8% (17 usec)
    new max. jitter: 1.9% (18 usec)
    new max. jitter: 3.9% (37 usec)
    threshold violated: 6.3% (61usec)
    new max. jitter: 6.3% (61 usec)
    threshold violated: 28.0% (273usec)
    new max. jitter: 28.0% (273 usec)
    threshold violated: 25.0% (243usec)

    Esben

    > Esben
    >
    > diff -Naur wakeup.cc~ wakeup.cc
    > --- wakeup.cc~ 2004-12-10 13:41:59.000000000 +0100
    > +++ wakeup.cc 2005-06-21 22:28:53.000000000 +0200
    > @@ -359,8 +359,7 @@
    > cycles_t last_cycles_count;
    > double max_jitter = 0;
    >
    > - struct timespec pause;
    > - pause.tv_nsec = 10000;
    > + struct timespec pause = { 0, 10000};
    >
    > std::cout.flags(std::ios::fixed);
    > std::cout << std::setprecision(1);
    > @@ -428,7 +427,11 @@
    > if (max_number_of_irqs > 0 && total_num_of_irqs >= max_number_of_irqs)
    > stopit = true;
    > }
    > - nanosleep(&pause,0);
    > + if(nanosleep(&pause,0))
    > + {
    > + perror("nanosleep:");
    > + exit(1);
    > + }
    > }
    > std::cout << "done." << std::endl;
    > std::cout << "total # of irqs: " << total_num_of_irqs << std::endl;
    >
    >
    >

    -
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