Anthony Liguori <anthony@xxxxxxxxxxxxx> writes: > > On a modern Nehalem, I would be surprised if an MMIO exit handled in > the kernel was muck more than 2us. The hardware is getting very, very > fast. The trends here are very important to consider when we're > looking at architectures that we potentially are going to support for > a long time. When you talk about trends the trend for IO is also to get faster. An exit will be always more expensive than passing something from another CPU in shared memory. An exit is much more work, with lots of saved context and fundamentally synchronous, even with all the tricks hardware can do. And then there's the in kernel handler too. Shared memory passing from another CPU is a much cheaper operation and more likely to scale with IO rate improvements. The basic problem in this discussion seems to be the usual disconnect between working code (I understand Gregory has working code that demonstrates the performance advances he's claiming) versus unwritten optimizations. Unwritten code tends to always sound nicer, but it remains to be seen if it can deliver what it promises. >From a abstract stand point having efficient paravirtual IO interfaces seem attractive. I also personally don't see a big problem in having another set of virtual drivers -- Linux already has plenty (vmware, xen, virtio, power, s390-vm, ...) and it's not that they would be a particular maintenance burden impacting the kernel core. -Andi -- ak@xxxxxxxxxxxxxxx -- Speaking for myself only. -- 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
