On Thu, Jan 09, 2020 at 09:51:50PM +0100, Paolo Bonzini wrote: > On 09/01/20 20:13, Michael S. Tsirkin wrote: > > That's one of the reasons I called for using something > > resembling vring_packed_desc. > > In principle it could make sense to use the ring-wrap detection > mechanism from vring_packed_desc instead of the producer/consumer > indices. However, the element address/length indirection is unnecessary. > > Also, unlike virtio, KVM needs to know if there are N free entries (N is > ~512) before running a guest. I'm not sure if that is possible with > ring-wrap counters, while it's trivial with producer/consumer indices. > > Paolo Yes it's easy: just check whether current entry + 500 has been consumed. Unless scatter/father is used, but then the answer is simple - just don't use it :) -- MST
