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

On 20 Apr 2006, at 08:45, Jan Beulich wrote:

... and even worse when the interrupt belongs to a domU.

Have you heard anything from Intel on this? I am still hoping that there is a pattern which interrupt gets triggered by masking a certain other one, so a (perhaps more complex, but less impacting) fix could be derived...

Arun Sharma pointed out its the same problem that FreeBSD has been having (they also mask interrupt lines when the ISR is scheduled in an interrupt thread). The problem is caused *by design* on many chipsets -- the idea is that if the bootloader or OS does not know about ACPI and cannot find the IO-APICs then interrupt lines routed to those IO-APICs should have their interrupt fired on a legacy line (it so happens that this usually is also the line used by the USB controllers). They detect this by seeing if the IO-APIC RTE is masked. Many chipsets have no way to disable this mode of operation (no need for Linux and Windows -- when they detect and enable IO-APICs, they never mask active RTEs). So, basically, we're screwed and have to work around by delaying the EOI.

 -- Keir

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