On 2018年04月01日 22:12, Tiwei Bie wrote:
Hello everyone,
This RFC implements packed ring support for virtio driver.
The code was tested with DPDK vhost (testpmd/vhost-PMD) implemented
by Jens at http://dpdk.org/ml/archives/dev/2018-January/089417.html
Minor changes are needed for the vhost code, e.g. to kick the guest.
TODO:
- Refinements and bug fixes;
- Split into small patches;
- Test indirect descriptor support;
- Test/fix event suppression support;
- Test devices other than net;
RFC v1 -> RFC v2:
- Add indirect descriptor support - compile test only;
- Add event suppression supprt - compile test only;
- Move vring_packed_init() out of uapi (Jason, MST);
- Merge two loops into one in virtqueue_add_packed() (Jason);
- Split vring_unmap_one() for packed ring and split ring (Jason);
- Avoid using '%' operator (Jason);
- Rename free_head -> next_avail_idx (Jason);
- Add comments for virtio_wmb() in virtqueue_add_packed() (Jason);
- Some other refinements and bug fixes;
Thanks!
Signed-off-by: Tiwei Bie <tiwei.bie@xxxxxxxxx>
---
drivers/virtio/virtio_ring.c | 1094 +++++++++++++++++++++++++++++-------
include/linux/virtio_ring.h | 8 +-
include/uapi/linux/virtio_config.h | 12 +-
include/uapi/linux/virtio_ring.h | 61 ++
4 files changed, 980 insertions(+), 195 deletions(-)
diff --git a/drivers/virtio/virtio_ring.c b/drivers/virtio/virtio_ring.c
index 71458f493cf8..0515dca34d77 100644
--- a/drivers/virtio/virtio_ring.c
+++ b/drivers/virtio/virtio_ring.c
@@ -58,14 +58,15 @@
[...]
+
+ if (vq->indirect) {
+ u32 len;
+
+ desc = vq->desc_state[head].indir_desc;
+ /* Free the indirect table, if any, now that it's unmapped. */
+ if (!desc)
+ goto out;
+
+ len = virtio32_to_cpu(vq->vq.vdev,
+ vq->vring_packed.desc[head].len);
+
+ BUG_ON(!(vq->vring_packed.desc[head].flags &
+ cpu_to_virtio16(vq->vq.vdev, VRING_DESC_F_INDIRECT)));
It looks to me spec does not force to keep VRING_DESC_F_INDIRECT here.
So we can safely remove this BUG_ON() here.
+ BUG_ON(len == 0 || len % sizeof(struct vring_packed_desc));
Len could be ignored for used descriptor according to the spec, so we
need remove this BUG_ON() too.
The reason is we don't touch descriptor ring in the case of split, so
BUG_ON()s may help there.
+
+ for (j = 0; j < len / sizeof(struct vring_packed_desc); j++)
+ vring_unmap_one_packed(vq, &desc[j]);
+
+ kfree(desc);
+ vq->desc_state[head].indir_desc = NULL;
+ } else if (ctx) {
+ *ctx = vq->desc_state[head].indir_desc;
+ }
+
+out:
+ return vq->desc_state[head].num;
+}
+
+static inline bool more_used_split(const struct vring_virtqueue *vq)
{
return vq->last_used_idx != virtio16_to_cpu(vq->vq.vdev, vq->vring.used->idx);
}
+static inline bool more_used_packed(const struct vring_virtqueue *vq)
+{
+ u16 last_used, flags;
+ bool avail, used;
+
+ if (vq->vq.num_free == vq->vring_packed.num)
+ return false;
+
+ last_used = vq->last_used_idx;
+ flags = virtio16_to_cpu(vq->vq.vdev,
+ vq->vring_packed.desc[last_used].flags);
+ avail = flags & VRING_DESC_F_AVAIL(1);
+ used = flags & VRING_DESC_F_USED(1);
+
+ return avail == used;
+}
This looks interesting, spec said:
"
Thus VIRTQ_DESC_F_AVAIL and VIRTQ_DESC_F_USED bits are different for an
available descriptor and
equal for a used descriptor.
Note that this observation is mostly useful for sanity-checking as these
are necessary but not sufficient
conditions - for example, all descriptors are zero-initialized. To
detect used and available descriptors it is
possible for drivers and devices to keep track of the last observed
value of VIRTQ_DESC_F_USED/VIRTQ_-
DESC_F_AVAIL. Other techniques to detect
VIRTQ_DESC_F_AVAIL/VIRTQ_DESC_F_USED bit changes
might also be possible.
"
So it looks to me it was not sufficient, looking at the example codes in
spec, do we need to track last seen used_wrap_counter here?
Thanks
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