On Mon, Feb 25, 2013 at 11:00:21AM -0300, Marcelo Tosatti wrote: > > I see a couple of possible solutions: > > 1. Do what Avi said. Make KVM_IRQ_LINE_STATUS be synchronous. Cons: > > current QEMU uses KVM_IRQ_LINE_STATUS always and it means that it > > will be slow on newer kernels > > Can add a capability to QEMU and enable APICv selectively only > in newer QEMU, which can issue KVM_IRQ_LINE_STATUS on target vcpu > only when necessary (and KVM_IRQ_LINE otherwise).
Bad idea. What happens with mixed scenarios. > Even a lock serializing injection is not safe because ON bit is cleared > before XCHG(PIR, 0). Must do something heavier (such as running on > target vcpu context). Note always running on target vcpu is likely to be slower than no-APICv. So need to do something heavier on the kernel under serialization, if firmware cannot be changed (injection from simultaneous CPUs should be rare so if data to serialize __accept_apic_irq is cache-line aligned it should reduce performance impact). > > 2. Make KVM_IRQ_LINE_STATUS report coalescing only when vcpu is not > > running during injection. This assumes that if vcpu is running and does > > not process interrupt it is guest fault and the same can happen on real > > HW too. Coalescing when vcpu is not running though is the result of CPU > > overcommit and should be reported. Cons interface definition is kind of > > murky. > > 3. Do not report KVM_IRQ_LINE_STATUS capability and move RTC to use EOI > > notifiers for interrupt reinjection. This requires us to add interface > > for reporting EOI to userspace. This is not in the scope of this > > patchset. Cons: need to introduce new interface (and the one that will > > not work on AMD BTW) Is there no int-ack notification at RTC HW level? > Breaks older userspace? > > > > Other ideas? > > Can HW write a 'finished' bit after 6 in the reserved area? Suppose its > not a KVM-specific problem? > -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
