Re: [PATCH 9/11] Panic delay fix

[Zachary Amsden <zach@vmware.com>]

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.

Zach