The goal of these patches is to add support to a variety of virtio and vhost devices for the VIRTIO_F_IN_ORDER transport feature. This feature indicates that all buffers are used by the device in the same order in which they were made available by the driver.
These patches attempt to implement a generalized, non-device-specific solution to support this feature. The core feature behind this solution is a buffer mechanism in the form of a VirtQueue's used_elems VirtQueueElement array. This allows devices who always use buffers in-order by default to have a minimal overhead impact. Devices that may not always use buffers in-order likely will experience a performance hit. How large that performance hit is will depend on how frequent elements are completed out-of-order. A VirtQueue whose device who uses this feature will use its used_elems VirtQueueElement array to hold used VirtQueueElements. The index that used elements are placed in used_elems is the same index on the used/descriptor ring that would satisfy the in-order requirement. In other words, used elements are placed in their in-order locations on used_elems and are only written to the used/descriptor ring once the elements on used_elems are able to continue their expected order. To differentiate between a "used" and "unused" element on the used_elems array (a "used" element being an element that has returned from processing and an "unused" element being an element that has not yet been processed), we added a boolean 'filled' member to the VirtQueueElement struct. This flag is set to true when the element comes back from processing (virtqueue_ordered_fill) and then set back to false once it's been written to the used/descriptor ring (virtqueue_ordered_flush). --- v1: Move series from RFC to PATCH for submission. Jonah Palmer (6): virtio: Add bool to VirtQueueElement virtio: virtqueue_pop - VIRTIO_F_IN_ORDER support virtio: virtqueue_ordered_fill - VIRTIO_F_IN_ORDER support virtio: virtqueue_ordered_flush - VIRTIO_F_IN_ORDER support vhost,vhost-user: Add VIRTIO_F_IN_ORDER to vhost feature bits virtio: Add VIRTIO_F_IN_ORDER property definition hw/block/vhost-user-blk.c | 1 + hw/net/vhost_net.c | 2 + hw/scsi/vhost-scsi.c | 1 + hw/scsi/vhost-user-scsi.c | 1 + hw/virtio/vhost-user-fs.c | 1 + hw/virtio/vhost-user-vsock.c | 1 + hw/virtio/virtio.c | 118 ++++++++++++++++++++++++++++++++++- include/hw/virtio/virtio.h | 5 +- net/vhost-vdpa.c | 1 + 9 files changed, 127 insertions(+), 4 deletions(-) -- 2.39.3
