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    SubjectRe: Realtime Preemption, 2.6.12, Beginners Guide?

    * Alistair John Strachan <s0348365@sms.ed.ac.uk> wrote:

    > Well, just to let others who have this problem know, it's clear that
    > Ingo's rt-preempt patches increase stack pressure on systems (like
    > mine) where stack is borderline under 4K by default.
    >
    > If you disable CONFIG_4KSTACKS the stack overflows seem to disappear.
    > As a result, until we isolate the problem, it'd probably be better if
    > Ingo maintained an 8K stacks option in the rt-preempt patches assuming
    > Adrian Bunk's "kill !4KSTACKS" patch gets into mainline..

    Ok. Could you try to debug this some more? In the -51-17 patch i've
    implemented a new stack-overflow debugging feature: 'stack footprint
    maximum searching'. It is automatically active if you have
    CONFIG_LATENCY_TRACE and CONFIG_DEBUG_STACKOVERFLOW enabled. It will
    track and (if it can be done safely) print out maximum stack usage sites
    immediately. Hopefully this results in better stackdumps. It should
    print similar traces:

    ----------------------------->
    | new stack-footprint maximum: smartd/1747, 1768 bytes.
    ------------|
    [<c013c1b6>] check_raw_flags+0xb/0x55 (8)
    [<c013ebeb>] sub_preempt_count+0x1a/0x1c (8)
    [<c013cb28>] __mcount+0x6a/0x91 (28)
    [<c013c3ff>] irqs_disabled+0x8/0x19 (16)
    [<c013c7b5>] ____trace+0x9e/0x208 (4)
    [<c01142d8>] mcount+0x14/0x18 (24)
    [<c013c3ff>] irqs_disabled+0x8/0x19 (20)
    [<c013c7b5>] ____trace+0x9e/0x208 (8)
    [<c013f145>] trace_stop_sched_switched+0x40/0x17d (8)
    [...]

    i've written a separate, hopefully more robust stack-dumper which is
    used for the above traces. Perhaps in your overflow case it results in
    something usable.

    Ingo
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