Avi Kivity wrote: > On 07/05/2010 12:07 PM, Jan Kiszka wrote: >> >>> What about ack notifiers? Ask the APIC to notify you when an interrupt >>> is acked. That allows you to track the BSP, all cpus, or some subset. >>> Masking can be seen at the irq controller level. >>> >> So, if I understand you correctly, an IRQ state change that is ignored >> due to masking would invoke the ack notifier chain as well? >> > > No - the cpu doesn't ack, no ack notifier. > > We might need a separate mask notifier. Just add pomodoro sauce.
Mask notifiers would be a must, otherwise you cannot tell apart if an IRQ was not yet ack'ed or is actually masked. On the other hand... see below. > >>> It's more involved, but provides more information. >>> >> Well, it requires to establish ack notifier chains in parallel to the >> existing IRQ delivery routes. Definitely more invasive. >> > > Right, and need to plumb it twice, once for qemu and once for kvm. > > But my feeling is you get a lot more information out of it. That decoupling between state change and acknowledgment worries me. Dispatching a source to multiple sinks or sharing a sink between multiple source is no longer cleanly manageable this way. Just look at the route of some ISA IRQ on x86: You may get an 'ack' from IOAPIC side and a 'masked' from the ISA side (or vice versa). And the 'masked' will arrive earlier. Not really straightforward to handle, is it? Moreover, it requires a concrete algorithm that takes advantage from the 'ack' information bit (that should be the only additional information you gain) to justify the additional effort. A "might have some advantages" is not enough IMO. Do we have such an algorithm already? Jan -- Siemens AG, Corporate Technology, CT T DE IT 1 Corporate Competence Center Embedded Linux
