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

To: "Jan Beulich" <JBeulich@xxxxxxxxxx>
Subject: Re: [Xen-devel] noirqdebug_setup() in arch/i386/kernel/setup-xen.c
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 7 Apr 2006 10:59:51 +0100
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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).

The above scenario is reasonably rare, and especially if there are currently irq problems I think we should stop asserting noirqdebug automatically, at least for now in xen-unstable.

 -- Keir

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