Gregory Haskins wrote:
Won't this have scaling issues? One IRQ means one target vcpu.
Whereas I'd like virtio devices to span multiple queues, each queue
with its own MSI IRQ.
Hmm..you know I hadnt really thought of it that way, but you have a
point. To clarify, my design actually uses one IRQ per "eventq", where
we can have an arbitrary number of eventq's defined (note: today I only
define one eventq, however). An eventq is actually a shm-ring construct
where I can pass events up to the host like "device added" or "ring X
signaled". Each individual device based virtio-ring would then
aggregates "signal" events onto this eventq mechanism to actually inject
events to the host. Only the eventq itself injects an actual IRQ to the
assigned vcpu.
You will get get cachelines bounced around when events from different
devices are added to the queue. On the plus side, a single injection
can contain interrupts for multiple devices.
I'm not sure how useful this coalescing is; certainly you will never see
it on microbenchmarks, but that doesn't mean it's not useful.
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I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.
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