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[Xen-devel] Re: [PATCH][FIX] Possible fix for spurious interrupts

To: "Jan Beulich" <jbeulich@xxxxxxxxxx>
Subject: [Xen-devel] Re: [PATCH][FIX] Possible fix for spurious interrupts
From: Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>
Date: Fri, 14 Apr 2006 19:42:18 +0100
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On 14 Apr 2006, at 18:42, Jan Beulich wrote:

This looks questionable to me (even after your follow-up mails). You are, in this mode, ack-ing the interrupt before the handler even gets invoked. I would expect level triggered interrupts to fire again right away then if you don't manage to run the handling domain before re-enabling interrupts. Of course, I haven't seen your later attempts at fixing the
problem, but am I missing something here?

Yes, I ack *after* the handlers have executed. The ack is in the ->end handler.

This is dodgy too on Xen unfortunately. All lower priority interrupts are blocked until the driver domain sees fit to tell Xen it's finished ISR processing. But if a large proportion of x86 hardware is screwed with respect to IO-APIC masking then we have no choice but to get this scheme to work. I look forward to the day when MSI is ubiquitous.

 -- Keir

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