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    Subjecttimer queue is still influenced by network load
    Richard,
    I did a few experiments using the example (jiq, I changed jiffies
    to do_gettimeofday() ) from Linux Device
    Driver, 2nd version (p196).

    I have two machines m1 and m2. On m1, I run a timer queue (jiq)
    module. Then I download a big file from m1 to m2. The timings are
    different between before ftp and during ftp.

    ----------------------------------------
    before ftp
    ----------------------------------------
    time pid cpu command
    420590 1 0 0 swapper
    430580 1 0 0 swapper
    440579 1 0 0 swapper
    450579 1 0 0 swapper
    460579 1 0 0 swapper
    470579 1 0 0 swapper
    480579 1 0 0 swapper
    490579 1 0 0 swapper
    500579 1 0 0 swapper

    ----------------------------------------
    during ftp
    ----------------------------------------
    time pid cpu command
    370605 1524 0 in.ftpd
    380645 0 0 swapper
    390583 0 0 swapper
    400667 0 0 swapper
    410703 1524 0 in.ftpd
    420679 0 0 swapper
    430634 0 0 swapper
    440624 0 0 swapper
    450648 0 0 swapper



    It shows that
    timer queue is still not accurate. So
    the conclusion of " you're guaranteed that the queue will run at the next
    clock tick, thus eliminating latency caused by system load" is WRONG!!!

    What is your opinion?

    Xinwen Fu


    On Wed, 3 Jul 2002, Richard B. Johnson wrote:

    > On Wed, 3 Jul 2002, Xinwen - Fu wrote:
    >
    > > Hi, all,
    > > I'm curious that if a network card interrupt happens at the same
    > > time as the kernel timer expires, what will happen?
    > >
    > > It's said the kernel timer is guaranteed accurate. But if
    > > interrupts are not masked off, the network interrupt also should get
    > > response when a kernel timer expires. So I don't know who will preempt
    > > who.
    > >
    > > Thanks for information!
    > >
    > > Xinwen Fu
    >
    > The highest priority interrupt will get serviced first. It's the timer.
    > Interrupts are serviced in priority-order. Hardware "remembers" which
    > ones are pending so none are lost if some driver doesn't do something
    > stupid.
    >
    > Cheers,
    > Dick Johnson
    >
    > Penguin : Linux version 2.4.18 on an i686 machine (797.90 BogoMips).
    >
    > Windows-2000/Professional isn't.
    >
    >

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