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    SubjectRe: [patch] Real-Time Preemption, -RT-2.6.9-rc4-mm1-U5

    * Adam Heath <adam@doogie.org> wrote:

    > => dump-end timestamp 29144924
    >
    > The kernel is jsut getting ready to start init at this point(mounting
    > root), so I don't know if you are really interested in this high
    > latency trace, but I'm sending anyways.

    lets skip these for the time being, large runtime ones are the first
    ones to be squashed.

    > However, after I reset the threshold to 50(and got a few small traces), I got
    > this whopper.
    >
    > (XFree86/1129/CPU#0): new 4692 us maximum-latency critical section.
    > => started at timestamp 358506933: <call_console_drivers+0x76/0x140>
    > => ended at timestamp 358511625: <finish_task_switch+0x43/0xa0>
    > [<c0132480>] sub_preempt_count+0x60/0x90

    interesting - this could be a printk (trace) done in a critical section
    though. What does /proc/latency_trace tell, is it full of console code
    functions?

    one of the best ways to avoid the console-printk-ing overhead is to do a
    'dmesg -n 1' and reset the maximum back to 50. (i prefer to use the
    preempt_max_latency option not the preempt_thresh option.)

    > ps: I've never mentioned the hardware I am running. Athlon XP 2000, 1G ram,
    > 460G(usable) software raid5(3*250g ide)(plus boot 120G), LVM, extra
    > SiliconImage UDMA133 controller(mobo can only do 100).
    >
    > I'm not certain what kind of latencies to expect with this setup. I'm
    > tending to ignore <100us, at least for now.

    this setup shouldnt produce above-100 usec latencies with -U5 and
    PREEMPT_REALTIME.

    Ingo
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