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    SubjectInterrupts disabled for too long in printk

    I ran some experiments with my kernel tracer (LTTng :
    that showed missing interrupts. I wrote a small paper to show how to use my
    tracer to solve this kind of problem which I presented at the CE Linux Form
    last April.

    It shows that, when the serial console is activated, the following code disables
    interrupts for up to 15ms. On a system configured with a 250HZ timer (each 4ms),
    it means that 3 scheduler ticks are lost.

    In the current git :

    kernel/printk.c: release_console_sem()

    for ( ; ; ) {
    -----> spin_lock_irqsave(&logbuf_lock, flags);
    wake_klogd |= log_start - log_end;
    if (con_start == log_end)
    break; /* Nothing to print */
    _con_start = con_start;
    _log_end = log_end;
    con_start = log_end; /* Flush */
    call_console_drivers(_con_start, _log_end);
    -----> local_irq_restore(flags);

    I guess interrupts are disabled for a good reason (to protect this spinlock for
    being taken by a nested interrupt handler. One way I am thinking to fix this
    problem would be to do a spin try lock and fail if it is already taken.


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      Last update: 2006-06-03 13:22    [W:0.023 / U:9.332 seconds]
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