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Message-ID: <20250708064819.35282-3-jasowang@redhat.com>
Date: Tue, 8 Jul 2025 14:48:19 +0800
From: Jason Wang <jasowang@...hat.com>
To: mst@...hat.com,
jasowang@...hat.com,
eperezma@...hat.com
Cc: kvm@...r.kernel.org,
virtualization@...ts.linux.dev,
netdev@...r.kernel.org,
linux-kernel@...r.kernel.org,
jonah.palmer@...cle.com
Subject: [PATCH net-next 2/2] vhost_net: basic in_order support
This patch introduces basic in-order support for vhost-net. By
recording the number of batched buffers in an array when calling
`vhost_add_used_and_signal_n()`, we can reduce the number of userspace
accesses. Note that the vhost-net batching logic is kept as we still
count the number of buffers there.
Testing Results:
With testpmd:
- TX: txonly mode + vhost_net with XDP_DROP on TAP shows a 17.5%
improvement, from 4.75 Mpps to 5.35 Mpps.
- RX: No obvious improvements were observed.
With virtio-ring in-order experimental code in the guest:
- TX: pktgen in the guest + XDP_DROP on TAP shows a 19% improvement,
from 5.2 Mpps to 6.2 Mpps.
- RX: pktgen on TAP with vhost_net + XDP_DROP in the guest achieves a
6.1% improvement, from 3.47 Mpps to 3.61 Mpps.
Signed-off-by: Jason Wang <jasowang@...hat.com>
---
drivers/vhost/net.c | 86 ++++++++++++++++++++++++++++++++-------------
1 file changed, 61 insertions(+), 25 deletions(-)
diff --git a/drivers/vhost/net.c b/drivers/vhost/net.c
index 4f9c67f17b49..8ac994b3228a 100644
--- a/drivers/vhost/net.c
+++ b/drivers/vhost/net.c
@@ -74,7 +74,8 @@ enum {
(1ULL << VHOST_NET_F_VIRTIO_NET_HDR) |
(1ULL << VIRTIO_NET_F_MRG_RXBUF) |
(1ULL << VIRTIO_F_ACCESS_PLATFORM) |
- (1ULL << VIRTIO_F_RING_RESET)
+ (1ULL << VIRTIO_F_RING_RESET) |
+ (1ULL << VIRTIO_F_IN_ORDER)
};
enum {
@@ -450,7 +451,8 @@ static int vhost_net_enable_vq(struct vhost_net *n,
return vhost_poll_start(poll, sock->file);
}
-static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq)
+static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq,
+ unsigned int count)
{
struct vhost_virtqueue *vq = &nvq->vq;
struct vhost_dev *dev = vq->dev;
@@ -458,8 +460,8 @@ static void vhost_net_signal_used(struct vhost_net_virtqueue *nvq)
if (!nvq->done_idx)
return;
- vhost_add_used_and_signal_n(dev, vq, vq->heads, NULL,
- nvq->done_idx);
+ vhost_add_used_and_signal_n(dev, vq, vq->heads,
+ vq->nheads, count);
nvq->done_idx = 0;
}
@@ -468,6 +470,8 @@ static void vhost_tx_batch(struct vhost_net *net,
struct socket *sock,
struct msghdr *msghdr)
{
+ struct vhost_virtqueue *vq = &nvq->vq;
+ bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
struct tun_msg_ctl ctl = {
.type = TUN_MSG_PTR,
.num = nvq->batched_xdp,
@@ -475,6 +479,11 @@ static void vhost_tx_batch(struct vhost_net *net,
};
int i, err;
+ if (in_order) {
+ vq->heads[0].len = 0;
+ vq->nheads[0] = nvq->done_idx;
+ }
+
if (nvq->batched_xdp == 0)
goto signal_used;
@@ -496,7 +505,7 @@ static void vhost_tx_batch(struct vhost_net *net,
}
signal_used:
- vhost_net_signal_used(nvq);
+ vhost_net_signal_used(nvq, in_order ? 1 : nvq->done_idx);
nvq->batched_xdp = 0;
}
@@ -758,6 +767,7 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
int sent_pkts = 0;
bool sock_can_batch = (sock->sk->sk_sndbuf == INT_MAX);
bool busyloop_intr;
+ bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
do {
busyloop_intr = false;
@@ -794,11 +804,13 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
break;
}
- /* We can't build XDP buff, go for single
- * packet path but let's flush batched
- * packets.
- */
- vhost_tx_batch(net, nvq, sock, &msg);
+ if (nvq->batched_xdp) {
+ /* We can't build XDP buff, go for single
+ * packet path but let's flush batched
+ * packets.
+ */
+ vhost_tx_batch(net, nvq, sock, &msg);
+ }
msg.msg_control = NULL;
} else {
if (tx_can_batch(vq, total_len))
@@ -819,8 +831,12 @@ static void handle_tx_copy(struct vhost_net *net, struct socket *sock)
pr_debug("Truncated TX packet: len %d != %zd\n",
err, len);
done:
- vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
- vq->heads[nvq->done_idx].len = 0;
+ if (in_order) {
+ vq->heads[0].id = cpu_to_vhost32(vq, head);
+ } else {
+ vq->heads[nvq->done_idx].id = cpu_to_vhost32(vq, head);
+ vq->heads[nvq->done_idx].len = 0;
+ }
++nvq->done_idx;
} while (likely(!vhost_exceeds_weight(vq, ++sent_pkts, total_len)));
@@ -999,7 +1015,7 @@ static int peek_head_len(struct vhost_net_virtqueue *rvq, struct sock *sk)
}
static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
- bool *busyloop_intr)
+ bool *busyloop_intr, unsigned int count)
{
struct vhost_net_virtqueue *rnvq = &net->vqs[VHOST_NET_VQ_RX];
struct vhost_net_virtqueue *tnvq = &net->vqs[VHOST_NET_VQ_TX];
@@ -1009,7 +1025,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
if (!len && rvq->busyloop_timeout) {
/* Flush batched heads first */
- vhost_net_signal_used(rnvq);
+ vhost_net_signal_used(rnvq, count);
/* Both tx vq and rx socket were polled here */
vhost_net_busy_poll(net, rvq, tvq, busyloop_intr, true);
@@ -1021,7 +1037,7 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
/* This is a multi-buffer version of vhost_get_desc, that works if
* vq has read descriptors only.
- * @vq - the relevant virtqueue
+ * @nvq - the relevant vhost_net virtqueue
* @datalen - data length we'll be reading
* @iovcount - returned count of io vectors we fill
* @log - vhost log
@@ -1029,14 +1045,17 @@ static int vhost_net_rx_peek_head_len(struct vhost_net *net, struct sock *sk,
* @quota - headcount quota, 1 for big buffer
* returns number of buffer heads allocated, negative on error
*/
-static int get_rx_bufs(struct vhost_virtqueue *vq,
+static int get_rx_bufs(struct vhost_net_virtqueue *nvq,
struct vring_used_elem *heads,
+ u16 *nheads,
int datalen,
unsigned *iovcount,
struct vhost_log *log,
unsigned *log_num,
unsigned int quota)
{
+ struct vhost_virtqueue *vq = &nvq->vq;
+ bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
unsigned int out, in;
int seg = 0;
int headcount = 0;
@@ -1073,14 +1092,16 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
nlogs += *log_num;
log += *log_num;
}
- heads[headcount].id = cpu_to_vhost32(vq, d);
len = iov_length(vq->iov + seg, in);
- heads[headcount].len = cpu_to_vhost32(vq, len);
- datalen -= len;
+ if (!in_order) {
+ heads[headcount].id = cpu_to_vhost32(vq, d);
+ heads[headcount].len = cpu_to_vhost32(vq, len);
+ }
++headcount;
+ datalen -= len;
seg += in;
}
- heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
+
*iovcount = seg;
if (unlikely(log))
*log_num = nlogs;
@@ -1090,6 +1111,15 @@ static int get_rx_bufs(struct vhost_virtqueue *vq,
r = UIO_MAXIOV + 1;
goto err;
}
+
+ if (!in_order)
+ heads[headcount - 1].len = cpu_to_vhost32(vq, len + datalen);
+ else {
+ heads[0].len = cpu_to_vhost32(vq, len + datalen);
+ heads[0].id = cpu_to_vhost32(vq, d);
+ nheads[0] = headcount;
+ }
+
return headcount;
err:
vhost_discard_vq_desc(vq, headcount);
@@ -1102,6 +1132,8 @@ static void handle_rx(struct vhost_net *net)
{
struct vhost_net_virtqueue *nvq = &net->vqs[VHOST_NET_VQ_RX];
struct vhost_virtqueue *vq = &nvq->vq;
+ bool in_order = vhost_has_feature(vq, VIRTIO_F_IN_ORDER);
+ unsigned int count = 0;
unsigned in, log;
struct vhost_log *vq_log;
struct msghdr msg = {
@@ -1149,12 +1181,13 @@ static void handle_rx(struct vhost_net *net)
do {
sock_len = vhost_net_rx_peek_head_len(net, sock->sk,
- &busyloop_intr);
+ &busyloop_intr, count);
if (!sock_len)
break;
sock_len += sock_hlen;
vhost_len = sock_len + vhost_hlen;
- headcount = get_rx_bufs(vq, vq->heads + nvq->done_idx,
+ headcount = get_rx_bufs(nvq, vq->heads + count,
+ vq->nheads + count,
vhost_len, &in, vq_log, &log,
likely(mergeable) ? UIO_MAXIOV : 1);
/* On error, stop handling until the next kick. */
@@ -1230,8 +1263,11 @@ static void handle_rx(struct vhost_net *net)
goto out;
}
nvq->done_idx += headcount;
- if (nvq->done_idx > VHOST_NET_BATCH)
- vhost_net_signal_used(nvq);
+ count += in_order ? 1 : headcount;
+ if (nvq->done_idx > VHOST_NET_BATCH) {
+ vhost_net_signal_used(nvq, count);
+ count = 0;
+ }
if (unlikely(vq_log))
vhost_log_write(vq, vq_log, log, vhost_len,
vq->iov, in);
@@ -1243,7 +1279,7 @@ static void handle_rx(struct vhost_net *net)
else if (!sock_len)
vhost_net_enable_vq(net, vq);
out:
- vhost_net_signal_used(nvq);
+ vhost_net_signal_used(nvq, count);
mutex_unlock(&vq->mutex);
}
--
2.31.1
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