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    SubjectRe: [PATCH 9/11] Panic delay fix
    Andi Kleen wrote:
    > On Mon, Feb 05, 2007 at 07:53:30PM -0800, Zachary Amsden wrote:
    >> Failure to use real-time delay here causes the keyboard to become demonically
    >> possessed in the event of a kernel crash, with wildly blinking lights and
    >> unpredictable behavior. This has resulted in several injuries.
    > There must be a reason why it wasn't default before. Has this
    > reason changed?

    This only matters under paravirt; non-paravirt kernels and kernels
    running on native hardware will always behave properly.

    But paravirtualized kernels with fake devices have no need to udelay to
    accommodate slow hardware - the hardware is just virtual. The
    USE_REAL_TIME_DELAY define allows udelay to be specifically reverted
    back to being a real delay. There are only a couple cases where it
    matters - one is booting APs on SMP systems (there is a real delay
    before they come up), and one is any hardware that drives world
    interacting devices - such as keyboard LEDs in a panic loop.

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