Avi Kivity wrote: > On 10/21/2009 05:42 PM, Gregory Haskins wrote: >> I believe Avi, Michael, et. al. were in agreement with me on that design >> choice. I believe the reason is that there is no good way to do EOI/ACK >> feedback within the constraints of an eventfd pipe which would be >> required for the legacy pin-type interrupts. Therefore, we won't even >> bother trying. High-performance subsystems will use irqfd/msi, and >> legacy emulation can use the existing injection code (which includes the >> necessary feedback for ack/eoi). >> >> > > Right. But we don't actually prevent anyone using non-msi with irqfd, > which can trigger the bad lock usage from irq context, with a nice boom > afterwards. So we need to either prevent it during registration, or to > gracefully handle it afterwards. > Yeah, I was thinking about that after I initially responded to Gleb. I am thinking something along these lines: Provide a function that lets you query a GSI for whether it supports LOCKLESS or not. Then we can either do one of two things: 1) Check for the LOCKLESS attribute at irqfd registration, fail if not present 2) Cache the LOCKLESS attribute in the irqfd structure, and either go direct or defer to a workqueue depending on the flag. Thoughts? -Greg
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