On Wed, Mar 22, 2023 at 7:42 PM Cornelia Huck <cohuck@xxxxxxxxxx> wrote: > > On Wed, Mar 22 2023, "Michael S. Tsirkin" <mst@xxxxxxxxxx> wrote: > > > On Wed, Mar 22, 2023 at 05:10:31PM +0300, Viktor Prutyanov wrote: > >> According to VirtIO spec v1.2, VIRTIO_F_NOTIFICATION_DATA feature > >> indicates that the driver passes extra data along with the queue > >> notifications. > >> > >> In a split queue case, the extra data is 16-bit available index. In a > >> packed queue case, the extra data is 1-bit wrap counter and 15-bit > >> available index. > >> > >> Add support for this feature for MMIO, channel I/O and modern PCI > >> transports. > >> > >> Signed-off-by: Viktor Prutyanov <viktor@xxxxxxxxxx> > >> --- > >> v4: remove VP_NOTIFY macro and legacy PCI support, add > >> virtio_ccw_kvm_notify_with_data to virtio_ccw > >> v3: support feature in virtio_ccw, remove VM_NOTIFY, use avail_idx_shadow, > >> remove byte swap, rename to vring_notification_data > >> v2: reject the feature in virtio_ccw, replace __le32 with u32 > >> > >> Tested with disabled VIRTIO_F_NOTIFICATION_DATA on qemu-system-s390x > >> (virtio-blk-ccw), qemu-system-riscv64 (virtio-blk-device, > >> virtio-rng-device), qemu-system-x86_64 (virtio-blk-pci, virtio-net-pci) > >> to make sure nothing is broken. > >> Tested with enabled VIRTIO_F_NOTIFICATION_DATA on 64-bit RISC-V Linux > >> and my hardware implementation of virtio-rng. > > > > what did you test? virtio pci? mmio? guessing not ccw... > > > > Cornelia could you hack up something to quickly test ccw? > > Hm, I'm not entirely sure how notification data is supposed to be used > in real life -- Viktor, what is your virtio-rng implementation doing; > can this be hacked into all transports? In hardware implementation of split VirtIO queue, the notification data feature saves time on a memory request to avail_idx from the device side. I can definitely say about MMIO, but most likely it is also useful for PCI. It is also written here that this feature was added for efficiency: https://www.mail-archive.com/virtio-dev@xxxxxxxxxxxxxxxxxxxx/msg02728.html Also DPDK has support for this feature in VirtIO PCI: https://github.com/DPDK/dpdk/commit/7e72f3ec1a8abefd9321a61e484846e16177f5b1 > > (Also, if the other ccw folks have something handy, please speak up :) >
