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

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Message-ID: <d120d5000702070658l1c018565n34a6d8814a20184d@mail.gmail.com>
Date:	Wed, 7 Feb 2007 09:58:57 -0500
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
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

On 2/6/07, Zachary Amsden <zach@...are.com> wrote:
> 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.
>

I am confused - does i8042 talk to a virtual or real hardware here? In
any case I think you need to fix kernel/panic.c to have proper
(m)delay, not mess with i8042.

-- 
Dmitry
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