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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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