| Message ID | 20240408153408.3527586-1-jonah.palmer@oracle.com (mailing list archive) |
|---|---|
| Headers | show |
| Series | virtio,vhost: Add VIRTIO_F_IN_ORDER support | expand |
QE tested this series with packed=on/off, in_order=true and vhost=off under regression tests, everything are works fine. Tested-by: Lei Yang <leiyang@redhat.com> On Mon, Apr 8, 2024 at 11:34 PM Jonah Palmer <jonah.palmer@oracle.com> wrote: > > 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). > > --- > v3: Add elements to used_elems during virtqueue_split/packed_pop > Replace current_seq_idx usage with vq->last_avail_idx > Remove used_seq_idx, leverage used_idx and last_avail_idx for > searching used_elems > Remove seq_idx in VirtQueueElement > Add boolean to VirtQueueElement to signal element status > Add virtqueue_ordered_fill/flush functions for ordering > > v2: Use a VirtQueue's used_elems array as a buffer mechanism > > v1: Implement custom GLib GHashTable as a buffer mechanism > > 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 >
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). --- v3: Add elements to used_elems during virtqueue_split/packed_pop Replace current_seq_idx usage with vq->last_avail_idx Remove used_seq_idx, leverage used_idx and last_avail_idx for searching used_elems Remove seq_idx in VirtQueueElement Add boolean to VirtQueueElement to signal element status Add virtqueue_ordered_fill/flush functions for ordering v2: Use a VirtQueue's used_elems array as a buffer mechanism v1: Implement custom GLib GHashTable as a buffer mechanism 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(-)