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[RFC v3 0/6] virtio,vhost: Add VIRTIO_F_IN_ORDER support
From: |
Jonah Palmer |
Subject: |
[RFC v3 0/6] virtio,vhost: Add VIRTIO_F_IN_ORDER support |
Date: |
Mon, 8 Apr 2024 11:34:02 -0400 |
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
- [RFC v3 0/6] virtio,vhost: Add VIRTIO_F_IN_ORDER support,
Jonah Palmer <=
- [RFC v3 1/6] virtio: Add bool to VirtQueueElement, Jonah Palmer, 2024/04/08
- [RFC v3 3/6] virtio: virtqueue_ordered_fill - VIRTIO_F_IN_ORDER support, Jonah Palmer, 2024/04/08
- [RFC v3 2/6] virtio: virtqueue_pop - VIRTIO_F_IN_ORDER support, Jonah Palmer, 2024/04/08
- [RFC v3 6/6] virtio: Add VIRTIO_F_IN_ORDER property definition, Jonah Palmer, 2024/04/08
- [RFC v3 5/6] vhost, vhost-user: Add VIRTIO_F_IN_ORDER to vhost feature bits, Jonah Palmer, 2024/04/08
- [RFC v3 4/6] virtio: virtqueue_ordered_flush - VIRTIO_F_IN_ORDER support, Jonah Palmer, 2024/04/08
- Re: [RFC v3 0/6] virtio,vhost: Add VIRTIO_F_IN_ORDER support, Lei Yang, 2024/04/15