From: Ammar Yasser
Add a vhost argument to tap_send_frames_pasta(). Callers pass it to say
whether this send should go through vhost-net, and when it does sending
goes through tap_send_frames_vhost(), which takes a descriptor from the
queue shared with the kernel for each iov and points it at that iov's
base address, chaining the bufs_per_frame descriptors of a frame
together so the guest receives it in one go.
tx_reap() reclaims the descriptors the kernel has finished with, walking
each used chain to its end so that every descriptor in it is counted as
free again.
Signed-off-by: Eugenio Pérez
Signed-off-by: Ammar Yasser
---
tap.c | 145 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++--
1 file changed, 142 insertions(+), 3 deletions(-)
diff --git a/tap.c b/tap.c
index c730535..0f51e62 100644
--- a/tap.c
+++ b/tap.c
@@ -359,12 +359,146 @@ void tap_icmp6_send(const struct ctx *c,
tap_send_single(c, buf, l4len + ((char *)icmp6h - buf));
}
+/**
+ * tx_reap() - Reclaim the descriptors the kernel has already processed
+ */
+static void tx_reap(void)
+{
+ struct vring_used *used = &vring_used_all[1].used;
+ uint16_t used_idx = le16toh(used->idx);
+
+ smp_rmb();
+
+ /* increment last_used_idx until it reaches the kernel's used index */
+ while (vhost_vq_state[1].last_used_idx != used_idx) {
+ uint16_t last_used, desc_id;
+
+ last_used = vhost_vq_state[1].last_used_idx % VHOST_NDESCS;
+ desc_id = le32toh(used->ring[last_used].id);
+
+ for (;;) {
+ /* keep going until we find a descriptor without the
+ * next flag
+ */
+ vhost_vq_state[1].num_free++;
+ if (!(le16toh(vring_desc[1][desc_id].flags) &
+ VRING_DESC_F_NEXT))
+ break;
+
+ /* this descriptor wasn't the last, set desc_id to the
+ * next one and keep going
+ */
+ desc_id = le16toh(vring_desc[1][desc_id].next);
+ }
+
+ vhost_vq_state[1].last_used_idx++;
+ }
+}
+
+/**
+ * tap_send_frames_vhost() - Send multiple frames to the pasta tap
+ * @c: Execution context
+ * @iov: Array of buffers
+ * @bufs_per_frame: Number of buffers (iovec entries) per frame
+ * @nframes: Number of frames to send
+ *
+ * @iov must have total length @bufs_per_frame * @nframes, with each set of
+ * @bufs_per_frame contiguous buffers representing a single frame.
+ *
+ * Return: number of frames successfully sent
+ */
+static size_t tap_send_frames_vhost(const struct ctx *c,
+ const struct iovec *iov,
+ size_t bufs_per_frame, size_t nframes)
+{
+ struct vring_avail *avail = &vring_avail_all[1].avail;
+ size_t processed_frames = 0;
+ size_t i;
+
+ /* reclaim descriptors if we don't have enough available buffers to
+ * perform this send
+ */
+ if (vhost_vq_state[1].num_free < bufs_per_frame * nframes)
+ tx_reap();
+
+ for (i = 0; i < nframes; i++) {
+ uint16_t head;
+ size_t j;
+
+ /* it's likely that tx_reap returned to us less than
+ * bufs_per_frame descs
+ */
+ if (vhost_vq_state[1].num_free < bufs_per_frame)
+ break;
+
+ /* set the index of the avail ring in the tx queue to be our
+ * last_used_idx
+ */
+ head = vhost_vq_state[1].next_free % VHOST_NDESCS;
+ avail->ring[(avail->idx + i) % VHOST_NDESCS] = htole16(head);
+
+ /* we will be consuming bufs_per_frame descriptors for every
+ * frame, decrement the local num_free
+ */
+ vhost_vq_state[1].num_free -= bufs_per_frame;
+
+ for (j = 0; j < bufs_per_frame; ++j) {
+ uint16_t next = vhost_vq_state[1].next_free %
+ VHOST_NDESCS;
+ /* get the last_used_idx descriptor */
+ struct vring_desc *desc = &vring_desc[1][next];
+ const struct iovec *iov_i;
+
+ /* the iov variable contains the iovecs for all frames
+ * we will send. access a single fragment of a frame
+ * (each fragment is one of tcp_iov_parts) denoted by
+ * iov at index i (index of the frame being processed)
+ * * bufs_per_frame plus j (the index of the fragment
+ * being processed)
+ */
+ iov_i = &iov[i * bufs_per_frame + j];
+
+ /* set that descriptor's address to the base of the iov
+ * and set the VRING_DESC_F_NEXT flag on the descriptor
+ * if its not the last frame fragment, so that the
+ * guest would recieve the entire frame in one go.
+ */
+ desc->addr = (uint64_t)iov_i->iov_base;
+ desc->len = iov_i->iov_len;
+ desc->flags = (j == bufs_per_frame - 1) ?
+ 0 : htole16(VRING_DESC_F_NEXT);
+
+ vhost_vq_state[1].next_free++;
+ }
+
+ processed_frames++;
+ }
+
+ /* we didn't process any frames, no need to notify the kernel */
+ if (!processed_frames)
+ return 0;
+
+ smp_wmb();
+
+ /* we will have used nframes descriptor chains */
+ avail->idx = htole16(le16toh(avail->idx) + processed_frames);
+
+ vhost_kick(&vring_used_all[1].used, c->vhost.vq[1].kick_fd);
+
+ /* wait until the kernel finishes processing this send */
+ while (avail->idx != vring_used_all[1].used.idx)
+ ;
+
+ return processed_frames;
+}
+
/**
* tap_send_frames_pasta() - Send multiple frames to the pasta tap
* @c: Execution context
* @iov: Array of buffers
* @bufs_per_frame: Number of buffers (iovec entries) per frame
* @nframes: Number of frames to send
+ * @vhost: Send through vhost-net rather than writing to the tap
*
* @iov must have total length @bufs_per_frame * @nframes, with each set of
* @bufs_per_frame contiguous buffers representing a single frame.
@@ -375,11 +509,15 @@ void tap_icmp6_send(const struct ctx *c,
*/
static size_t tap_send_frames_pasta(const struct ctx *c,
const struct iovec *iov,
- size_t bufs_per_frame, size_t nframes)
+ size_t bufs_per_frame, size_t nframes,
+ bool vhost)
{
size_t nbufs = bufs_per_frame * nframes;
size_t i;
+ if (vhost)
+ return tap_send_frames_vhost(c, iov, bufs_per_frame, nframes);
+
for (i = 0; i < nbufs; i += bufs_per_frame) {
ssize_t rc = writev(c->fd_tap, iov + i, bufs_per_frame);
size_t framelen = iov_size(iov + i, bufs_per_frame);
@@ -515,7 +653,7 @@ void tap_send_single(const struct ctx *c, const void *data, size_t l2len)
iov[iovcnt].iov_len = l2len;
iovcnt++;
- m = tap_send_frames_pasta(c, iov, iovcnt, 1);
+ m = tap_send_frames_pasta(c, iov, iovcnt, 1, false);
break;
case MODE_VU:
vu_send_single(c, data, l2len);
@@ -553,7 +691,8 @@ size_t tap_send_frames(const struct ctx *c, const struct iovec *iov,
switch (c->mode) {
case MODE_PASTA:
- m = tap_send_frames_pasta(c, iov, bufs_per_frame, nframes);
+ m = tap_send_frames_pasta(c, iov, bufs_per_frame, nframes,
+ c->vhost.fd != -1);
break;
case MODE_PASST:
m = tap_send_frames_passt(c, iov, bufs_per_frame, nframes);
--
2.39.5 (Apple Git-154)