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Subject[PATCH net-next RFC 5/5] vhost_net: basic tx virtqueue batched processing
Date
This patch implements basic batched processing of tx virtqueue by
prefetching desc indices and updating used ring in a batch. For
non-zerocopy case, vq->heads were used for storing the prefetched
indices and updating used ring. It is also a requirement for doing
more batching on top. For zerocopy case and for simplicity, batched
processing were simply disabled by only fetching and processing one
descriptor at a time, this could be optimized in the future.

XDP_DROP (without touching skb) on tun (with Moongen in guest) with
zercopy disabled:

Intel(R) Xeon(R) CPU E5-2650 0 @ 2.00GHz:
Before: 3.20Mpps
After: 3.90Mpps (+22%)

No differences were seen with zerocopy enabled.

Signed-off-by: Jason Wang <jasowang@redhat.com>
---
drivers/vhost/net.c | 215 ++++++++++++++++++++++++++++----------------------
drivers/vhost/vhost.c | 2 +-
2 files changed, 121 insertions(+), 96 deletions(-)

diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index c89640e..c439892 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -408,27 +408,25 @@ static int vhost_net_enable_vq(struct vhost_net *n,
return vhost_poll_start(poll, sock->file);
}

-static int vhost_net_tx_get_vq_desc(struct vhost_net *net,
- struct vhost_virtqueue *vq,
- struct iovec iov[], unsigned int iov_size,
- unsigned int *out_num, unsigned int *in_num)
+static bool vhost_net_tx_avail(struct vhost_net *net,
+ struct vhost_virtqueue *vq)
{
unsigned long uninitialized_var(endtime);
- int r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
- out_num, in_num, NULL, NULL);

- if (r == vq->num && vq->busyloop_timeout) {
- preempt_disable();
- endtime = busy_clock() + vq->busyloop_timeout;
- while (vhost_can_busy_poll(vq->dev, endtime) &&
- vhost_vq_avail_empty(vq->dev, vq))
- cpu_relax();
- preempt_enable();
- r = vhost_get_vq_desc(vq, vq->iov, ARRAY_SIZE(vq->iov),
- out_num, in_num, NULL, NULL);
- }
+ if (!vq->busyloop_timeout)
+ return false;

- return r;
+ if (!vhost_vq_avail_empty(vq->dev, vq))
+ return true;
+
+ preempt_disable();
+ endtime = busy_clock() + vq->busyloop_timeout;
+ while (vhost_can_busy_poll(vq->dev, endtime) &&
+ vhost_vq_avail_empty(vq->dev, vq))
+ cpu_relax();
+ preempt_enable();
+
+ return !vhost_vq_avail_empty(vq->dev, vq);
}

static bool vhost_exceeds_maxpend(struct vhost_net *net)
@@ -446,8 +444,9 @@ static void handle_tx(struct vhost_net *net)
{
struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_TX];
struct vhost_virtqueue *vq = &nvq->vq;
+ struct vring_used_elem used, *heads = vq->heads;
unsigned out, in;
- int head;
+ int avails, head;
struct msghdr msg = {
.msg_name = NULL,
.msg_namelen = 0,
@@ -461,6 +460,7 @@ static void handle_tx(struct vhost_net *net)
struct socket *sock;
struct vhost_net_ubuf_ref *uninitialized_var(ubufs);
bool zcopy, zcopy_used;
+ int i, batched = VHOST_NET_BATCH;

mutex_lock(&vq->mutex);
sock = vq->private_data;
@@ -475,6 +475,12 @@ static void handle_tx(struct vhost_net *net)
hdr_size = nvq->vhost_hlen;
zcopy = nvq->ubufs;

+ /* Disable zerocopy batched fetching for simplicity */
+ if (zcopy) {
+ heads = &used;
+ batched = 1;
+ }
+
for (;;) {
/* Release DMAs done buffers first */
if (zcopy)
@@ -486,95 +492,114 @@ static void handle_tx(struct vhost_net *net)
if (unlikely(vhost_exceeds_maxpend(net)))
break;

- head = vhost_net_tx_get_vq_desc(net, vq, vq->iov,
- ARRAY_SIZE(vq->iov),
- &out, &in);
+ avails = vhost_prefetch_desc_indices(vq, heads, batched, !zcopy);
/* On error, stop handling until the next kick. */
- if (unlikely(head < 0))
+ if (unlikely(avails < 0))
break;
- /* Nothing new? Wait for eventfd to tell us they refilled. */
- if (head == vq->num) {
+ /* Nothing new? Busy poll for a while or wait for
+ * eventfd to tell us they refilled. */
+ if (!avails) {
+ if (vhost_net_tx_avail(net, vq))
+ continue;
if (unlikely(vhost_enable_notify(&net->dev, vq))) {
vhost_disable_notify(&net->dev, vq);
continue;
}
break;
}
- if (in) {
- vq_err(vq, "Unexpected descriptor format for TX: "
- "out %d, int %d\n", out, in);
- break;
- }
- /* Skip header. TODO: support TSO. */
- len = iov_length(vq->iov, out);
- iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
- iov_iter_advance(&msg.msg_iter, hdr_size);
- /* Sanity check */
- if (!msg_data_left(&msg)) {
- vq_err(vq, "Unexpected header len for TX: "
- "%zd expected %zd\n",
- len, hdr_size);
- break;
- }
- len = msg_data_left(&msg);
-
- zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
- && (nvq->upend_idx + 1) % UIO_MAXIOV !=
- nvq->done_idx
- && vhost_net_tx_select_zcopy(net);
-
- /* use msg_control to pass vhost zerocopy ubuf info to skb */
- if (zcopy_used) {
- struct ubuf_info *ubuf;
- ubuf = nvq->ubuf_info + nvq->upend_idx;
-
- vq->heads[nvq->upend_idx].id = cpu_to_vhost32(vq, head);
- vq->heads[nvq->upend_idx].len = VHOST_DMA_IN_PROGRESS;
- ubuf->callback = vhost_zerocopy_callback;
- ubuf->ctx = nvq->ubufs;
- ubuf->desc = nvq->upend_idx;
- refcount_set(&ubuf->refcnt, 1);
- msg.msg_control = ubuf;
- msg.msg_controllen = sizeof(ubuf);
- ubufs = nvq->ubufs;
- atomic_inc(&ubufs->refcount);
- nvq->upend_idx = (nvq->upend_idx + 1) % UIO_MAXIOV;
- } else {
- msg.msg_control = NULL;
- ubufs = NULL;
- }
+ for (i = 0; i < avails; i++) {
+ head = __vhost_get_vq_desc(vq, vq->iov,
+ ARRAY_SIZE(vq->iov),
+ &out, &in, NULL, NULL,
+ vhost16_to_cpu(vq, heads[i].id));
+ if (in) {
+ vq_err(vq, "Unexpected descriptor format for "
+ "TX: out %d, int %d\n", out, in);
+ goto out;
+ }

- total_len += len;
- if (total_len < VHOST_NET_WEIGHT &&
- !vhost_vq_avail_empty(&net->dev, vq) &&
- likely(!vhost_exceeds_maxpend(net))) {
- msg.msg_flags |= MSG_MORE;
- } else {
- msg.msg_flags &= ~MSG_MORE;
- }
+ /* Skip header. TODO: support TSO. */
+ len = iov_length(vq->iov, out);
+ iov_iter_init(&msg.msg_iter, WRITE, vq->iov, out, len);
+ iov_iter_advance(&msg.msg_iter, hdr_size);
+ /* Sanity check */
+ if (!msg_data_left(&msg)) {
+ vq_err(vq, "Unexpected header len for TX: "
+ "%zd expected %zd\n",
+ len, hdr_size);
+ goto out;
+ }
+ len = msg_data_left(&msg);

- /* TODO: Check specific error and bomb out unless ENOBUFS? */
- err = sock->ops->sendmsg(sock, &msg, len);
- if (unlikely(err < 0)) {
+ zcopy_used = zcopy && len >= VHOST_GOODCOPY_LEN
+ && (nvq->upend_idx + 1) % UIO_MAXIOV !=
+ nvq->done_idx
+ && vhost_net_tx_select_zcopy(net);
+
+ /* use msg_control to pass vhost zerocopy ubuf
+ * info to skb
+ */
if (zcopy_used) {
- vhost_net_ubuf_put(ubufs);
- nvq->upend_idx = ((unsigned)nvq->upend_idx - 1)
- % UIO_MAXIOV;
+ struct ubuf_info *ubuf;
+ ubuf = nvq->ubuf_info + nvq->upend_idx;
+
+ vq->heads[nvq->upend_idx].id =
+ cpu_to_vhost32(vq, head);
+ vq->heads[nvq->upend_idx].len =
+ VHOST_DMA_IN_PROGRESS;
+ ubuf->callback = vhost_zerocopy_callback;
+ ubuf->ctx = nvq->ubufs;
+ ubuf->desc = nvq->upend_idx;
+ refcount_set(&ubuf->refcnt, 1);
+ msg.msg_control = ubuf;
+ msg.msg_controllen = sizeof(ubuf);
+ ubufs = nvq->ubufs;
+ atomic_inc(&ubufs->refcount);
+ nvq->upend_idx =
+ (nvq->upend_idx + 1) % UIO_MAXIOV;
+ } else {
+ msg.msg_control = NULL;
+ ubufs = NULL;
+ }
+
+ total_len += len;
+ if (total_len < VHOST_NET_WEIGHT &&
+ !vhost_vq_avail_empty(&net->dev, vq) &&
+ likely(!vhost_exceeds_maxpend(net))) {
+ msg.msg_flags |= MSG_MORE;
+ } else {
+ msg.msg_flags &= ~MSG_MORE;
+ }
+
+ /* TODO: Check specific error and bomb out
+ * unless ENOBUFS?
+ */
+ err = sock->ops->sendmsg(sock, &msg, len);
+ if (unlikely(err < 0)) {
+ if (zcopy_used) {
+ vhost_net_ubuf_put(ubufs);
+ nvq->upend_idx =
+ ((unsigned)nvq->upend_idx - 1) % UIO_MAXIOV;
+ }
+ vhost_discard_vq_desc(vq, 1);
+ goto out;
+ }
+ if (err != len)
+ pr_debug("Truncated TX packet: "
+ " len %d != %zd\n", err, len);
+ if (!zcopy) {
+ vhost_add_used_idx(vq, 1);
+ vhost_signal(&net->dev, vq);
+ } else if (!zcopy_used) {
+ vhost_add_used_and_signal(&net->dev,
+ vq, head, 0);
+ } else
+ vhost_zerocopy_signal_used(net, vq);
+ vhost_net_tx_packet(net);
+ if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
+ vhost_poll_queue(&vq->poll);
+ goto out;
}
- vhost_discard_vq_desc(vq, 1);
- break;
- }
- if (err != len)
- pr_debug("Truncated TX packet: "
- " len %d != %zd\n", err, len);
- if (!zcopy_used)
- vhost_add_used_and_signal(&net->dev, vq, head, 0);
- else
- vhost_zerocopy_signal_used(net, vq);
- vhost_net_tx_packet(net);
- if (unlikely(total_len >= VHOST_NET_WEIGHT)) {
- vhost_poll_queue(&vq->poll);
- break;
}
}
out:
diff --git a/drivers/vhost/vhost.c b/drivers/vhost/vhost.c
index 6532cda..8764df5 100644
--- a/drivers/vhost/vhost.c
+++ b/drivers/vhost/vhost.c
@@ -392,7 +392,7 @@ static long vhost_dev_alloc_iovecs(struct vhost_dev *dev)
vq->indirect = kmalloc(sizeof *vq->indirect * UIO_MAXIOV,
GFP_KERNEL);
vq->log = kmalloc(sizeof *vq->log * UIO_MAXIOV, GFP_KERNEL);
- vq->heads = kmalloc(sizeof *vq->heads * UIO_MAXIOV, GFP_KERNEL);
+ vq->heads = kzalloc(sizeof *vq->heads * UIO_MAXIOV, GFP_KERNEL);
if (!vq->indirect || !vq->log || !vq->heads)
goto err_nomem;
}
--
2.7.4
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