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    SubjectRe: How how latent should non-preemptive scheduling be?

    * Sitsofe Wheeler <sitsofe@yahoo.com> wrote:

    > Logs with the filtering on can be seen here (15Mbytes decompressed each):
    > http://sucs.org/~sits/test/eeepc-debug/20080923/latency_trace.gz
    > http://sucs.org/~sits/test/eeepc-debug/20080923/trace.txt.gz
    >
    > It looks like lots of acpi state is created and deleted...

    yeah. The latency starts here:

    cat-5901 0dNh. 1us : default_wake_function (__wake_up_common)
    cat-5901 0.Nh. 2us : kill_fasync (snd_pcm_period_elapsed)
    [...]

    and ends here:

    [...]
    cat-5901 0.N.. 270501us+: mutex_lock (acpi_ec_transaction)
    cat-5901 0d... 270507us : __cond_resched (_cond_resched)

    270 _milliseconds_ later. That's excessive.

    The main overhead is starting here:

    cat-5901 0.N.. 167us : acpi_ds_result_push (acpi_ds_exec_end_op)

    lots of ACPI code executed ...

    does it get better if you have CONFIG_PREEMPT_VOLUNTARY=y enabled? That
    _should_ break up this section neatly. If it doesnt then please add a
    might_sleep() check to kernel/kernel/semaphore.c's down_timeout()
    function - that is called a number of times in this trace.

    Ingo


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