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    SubjectRe: 2.6.24-rc6-git12: Reported regressions from 2.6.23
    On Sun, 6 Jan 2008 10:55:01 +0100
    Ingo Molnar <mingo@elte.hu> wrote:

    >
    > * Mark Lord <lkml@rtr.ca> wrote:
    >
    > > Rafael J. Wysocki wrote:
    > >> This message contains a list of some regressions from 2.6.23
    > >> reported since 2.6.24-rc1 was released, for which there are no
    > >> fixes in the mainline I know of. If any of them have been fixed
    > >> already, please let me know.
    > > ..
    > >> Subject : 20000+ wake-ups/second in 2.6.24
    > >> Submitter : Mark Lord <lkml@rtr.ca>
    > >> Date : 2007-12-02 04:23
    > >> References : http://lkml.org/lkml/2007/12/1/141
    > >> http://bugzilla.kernel.org/show_bug.cgi?id=9489
    > >> Handled-By : Arjan van de Ven <arjan@infradead.org>
    > >>
    > >
    > > I wonder if it's just a babbling IRQ on resume, before the driver
    > > has run it's resume code or something ?
    >
    > i've read the discussions, and i cannot see it analyzed anywhere
    > _what_ causes the wakeups. And how are these wakeups counted? Is this
    > based on powertop output:
    >
    > Wakeups-from-idle per second : 20.4 interval: 1.8s
    >
    > ? Somewhere i saw it mentioned that "the CPU throws out of C mode".
    > What does that mean - does it mean we try to idle again and again,
    > but we immediately return from C mode - while this all looks like
    > "idle" time to the scheduler (so 'top' will show lots of idle time),
    > but the ACPI wakeup counters are going up like mad? What
    > is /proc/interrupts doing when this happens - is any of the irq
    > sources going upwards?
    >

    what seems to happen (and this is based on seeing this on my own devel laptop, as well
    as several other reports; Mark is by far not the only one) is something hardware
    related, it's been seen on lots of different kernel versions.

    It seems to mostly (but not 100%) happen with TI cardbus bridges, where for some reason,
    once the yenta driver is loaded (unloading it later makes no difference), once in a while
    we get into a mode where the CPU always immediately goes out of the C-state again.
    On a hardware level, there are only a few things that cause a CPU to exit a C-state,
    and one of them is a pending interrupt of some kind, which is the most likely thing going on here;
    some device or apic being stuck with interrupt high, but somehow the CPU isn't actually
    seeing the interrupt itself (or has it blocked!)

    To call this a 2.6.24 regression is a mistake (as I've said before), it's not new to .24
    by any means.

    --
    If you want to reach me at my work email, use arjan@linux.intel.com
    For development, discussion and tips for power savings,
    visit http://www.lesswatts.org


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