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

[Keir Fraser <Keir.Fraser@xxxxxxxxxxxx>]

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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