Re: [PATCH 9/11] Panic delay fix

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On 8 Feb 2007 14:33:21 +0100, Andi Kleen <[email protected]> wrote:
On Thu, Feb 08, 2007 at 01:08:14AM -0800, Zachary Amsden wrote:
> Andi Kleen wrote:
> >On Wed, Feb 07, 2007 at 02:31:57PM -0800, Zachary Amsden wrote:
> >
> >>Dmitry Torokhov wrote:
> >>
> >>>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.
> >>>
> >>I think I need to fix both of them actually.  This is virtual hardware,
> >>but when you grab focus on a VM, the virtual hardware gets reflected to
> >>the actual physical keyboard.  Driving physical hardware that fast is bad.
> >>
> >
> >???
> >
> >Surely the physical keyboard is always handled by the host kernel?
> >I hope you're not saying it's trying to access the io ports directly?
> >
>
> No, not that.  But the virtual keyboard I/O gets processed and converted
> to physical keyboard I/O when a keyboard is attached to a VM.  The

You mean the commands to change the keyboard LEDs?

> result is that the virtual keyboard spinning out of control causes the
> physical keyboard to receive the same commands, far too rapidly.

Hmm i would expect the host kernel keyboard driver to throttle these.
I'm pretty sure the Linux one does the necessary mdelays at least.

There is no throttling, we will switch leds as fast as keyboard
controller will allow us (not that I consider it a bad thing).


> So the keyboard blinks out of control and acts as if possessed by demons.

Still sounds weird.


The problem is that panic blink routine expects to be called with 1ms
frequency. If mdelay in kernel/panic.c is changed to noop then i8042
will try to blink as fast as it possibly can.

--
Dmitry
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