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Re: [Xen-devel] noirqdebug_setup() in arch/i386/kernel/setup-xen.c

To: "Keir Fraser" <Keir.Fraser@xxxxxxxxxxxx>
Subject: Re: [Xen-devel] noirqdebug_setup() in arch/i386/kernel/setup-xen.c
From: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Date: Fri, 07 Apr 2006 12:15:31 +0200
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>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 07.04.06 11:59:51 >>>
>On 7 Apr 2006, at 10:00, Jan Beulich wrote:
>> Can anyone explain why i386 calls noirqdebug_setup() unconditionally, 
>> while x86-64 doesn't? I believe this is the reason
>> why we have been seeing spurious interrupt reports only on 64-bits so 
>> far.
>> What was this supposed to suppress originally? Is this still 
>> applicable? It would seem to me that hiding problems in
>> this area is rather undesirable...
>It's disabled to handle the case where a shared IRQ line is shared 
>across multiple driver domains. In that case, if one domain's device is 
>busy then both domains will get interrupt notifications, but the 
>non-busy driver domain will think that it's receiving spurious 
>interrupts (since it doesn't see IRQ_HANDLED from the busy device 
>driver ISR, since it's running in a different driver domain).

Then, once we are able to figure the interrupt problems we currently have, this 
should probably be re-enabled
temporarily and for *all* architectures, but be replaced by proper logic (i.e. 
Xen informing the domain e.g. by means of
a flag passed with the injected IRQ that it should expect the interrupt to not 
getting handled; Xen should then also
expect some notification back from the domain that the IRQ was handled, so it 
can combine this from all involved domains
and still report and act on problems similar to the way Linux does).


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