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    SubjectRe: wake_up() takes long time to return
    On 1/20/07, Arjan van de Ven <> wrote:
    > On Sat, 2007-01-20 at 15:54 +0530, kalash nainwal wrote:
    > > Hi there,
    > >
    > > We've a kernel (n/w) module, which sits over ethernet. Whenever a pkt
    > > is received (in softirq), after doing some minimal processing,
    > > wake_up() is called to wake up another kernel thread which does rest
    > > (bulk) of the processing.
    > >
    > > We notice that this wake_up() call is sometimes taking as long as 48
    > > milli-seconds to return. This happens around 10 times out of 10M. We
    > > earlier thought its possibly because of the contention on rq->lock,
    > > but we see the same phenomenon even on a uniprocessor box. So obviosly
    > > thats not the case.
    > >
    > > We can't figure out any other reason for wake_up() to take this much
    > > time? As this call comes directly in our (receive) hotpath, we're very
    > > concerned. Any help would be greatly appreciated.
    > Hi,
    > unfortunately you didn't provide your driver code or a link to it, so
    > people who want to help you would have to guess in the dark... could you
    > reply to this email with the pointer to the code?
    > Greetings,
    > Arjan van de Ven
    > --
    > if you want to mail me at work (you don't), use arjan (at)
    > Test the interaction between Linux and your BIOS via

    Hi Arjan,

    I won't pretend I'm working on an open-source driver. I personally
    would be more than happy to share the driver code, but doing so would
    probably cost me my job :)

    and so...I won't expect anyone to help me with my code either.

    Just wanted to know if wake_up is known to take this long to return?
    (some known linux quirk may be?) If so then under what conditions? or
    it _definitely_ would be my code only that's screwing up?

    I'm using do_gettimeofday() before and after wake_up() to measure this time.

    Thanks and regards,
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