linux-kernel - Re: [PATCH 9/11] Panic delay fix

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Message-ID: <20070207123552.GD4481@ucw.cz>
Date:	Wed, 7 Feb 2007 12:35:52 +0000
From:	Pavel Machek <pavel@....cz>
To:	Zachary Amsden <zach@...are.com>
Cc:	Andi Kleen <ak@....de>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...l.org>,
	Rusty Russell <rusty@...tcorp.com.au>,
	Jeremy Fitzhardinge <jeremy@...p.org>,
	Chris Wright <chrisw@...s-sol.org>
Subject: Re: [PATCH 9/11] Panic delay fix

Hi!
> >  
> >>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 

Ugh, it sounds like paravirt is more b0rken then I thought. It should
always to the proper delay, then replace those udelays that are not
needed on virtualized hardware with something else.

Just magically defining udelay into nop is broken.

							Pavel
-- 
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures) http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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