Hi, here's a proposal to support adapter (aka thin) interrupts for virtio-ccw. The basic idea is to make host->guest signalling on s390 more lightweight. Normal I/O interrupts have two parts: an interrupt that is made pending on any of the guest cpus, and status that is made pending on the subchannel. This means that we need two exits for every interrupt. With adapter interrupts, only the I/O interrupt remains - no status is made pending for the subchannel. To find out which virtqueue the signal was for we rely on indicators. To set this up, the guest uses a new ccw (which is used instead of the normal ccw to set up indicators). The payload contains pointers to two indicators (first level and second level) and the offset at which the virtqueue indicators start in the second level indicators, as well as the interruption subclass (which will usually be the same as the isc for the device). This is partially inspired by what qdio does today. I have seen some nice speedup on simple dd with my current implementation. Adapter interrupts are also a prereq for implementing irqfd on s390, since they eliminate the need for manipulating subchannel status. Cornelia Huck (1): virtio-ccw: Document adapter interrupts. virtio-spec.lyx | 147 +++++++++++++++++++++++++++++++++++++++++++++++++++++-- 1 file changed, 144 insertions(+), 3 deletions(-) -- 1.7.9.5 -- To unsubscribe from this list: send the line "unsubscribe kvm" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
