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

["Jan Beulich" <jbeulich@xxxxxxxxxx>]

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?


Jan
>>> Keir Fraser <Keir.Fraser@xxxxxxxxxxxx> 04/13/06 8:12 PM >>>

Here is a patch that appears to fix the spurious interrupt problems for 
me. This is inspired by Jan's observation that the IO-APIC mask/unmask 
that we do for ISR processing seems to cause corruption of other 
routing entries. So the fix here is to do the same as native Linux -- 
do not mask/unmask, but instead send EOI after doing ISR processing.

To confirm this really was the problem I modified native Linux to do 
the same as Xen currently does (mask before ISR processing; unmask 
after). I then got lots of spurious USB interrupts even on native 
Linux! :-(

Please test... I'll put it in xen-unstable tomorrow if there are no 
complaints and it will be a strong candidate for the next 3.0.2 release 
too.

  -- Keir



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