* [PATCH v2] hw/net/virtio-net: add support for notification coalescing
@ 2026-03-11 13:28 Koushik Dutta
2026-03-12 10:17 ` Eugenio Perez Martin
0 siblings, 1 reply; 4+ messages in thread
From: Koushik Dutta @ 2026-03-11 13:28 UTC (permalink / raw)
To: qemu-devel
Cc: Stefano Garzarella, Michael S. Tsirkin, Eugenio Pérez,
Jason Wang
Implement VirtIO Network Notification Coalescing (Bit 53).
This allows the guest to manage interrupt frequency using ethtool
-C for both RX and TX paths.
- Added VIRTIO_NET_F_NOTF_COAL to host features.
- Implemented VIRTIO_NET_CTRL_NOTF_COAL class handling in
virtio_net_handle_ctrl_iov.
- Added logic to store and apply rx/tx usecs and max_packets.
- Added packet counters and threshold logic for both RX and TX data paths.
- Dynamic Dispatcher: Implemented a dispatcher mechanism that
dynamically switches/activates the notification callback logic
only after the guest enables TX coalescing via ethtool.
This reduces interrupt overhead by batching notifications based on
either a packet count or a time-based threshold.
Signed-off-by: Koushik Dutta <kdutta@redhat.com>
---
hw/net/virtio-net.c | 114 ++++++++++++++++++++++++-----
hw/virtio/vhost-shadow-virtqueue.c | 1 +
hw/virtio/vhost-vdpa.c | 3 +
include/hw/virtio/virtio-net.h | 8 ++
net/vhost-vdpa.c | 10 +++
5 files changed, 119 insertions(+), 17 deletions(-)
diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
index eccb48ad42..96aa70aea8 100644
--- a/hw/net/virtio-net.c
+++ b/hw/net/virtio-net.c
@@ -157,6 +157,15 @@ static void flush_or_purge_queued_packets(NetClientState *nc)
* - we could suppress RX interrupt if we were so inclined.
*/
+static void virtio_net_rx_notify(void *opaque)
+{
+ VirtIONet *n = opaque;
+ VirtIODevice *vdev = VIRTIO_DEVICE(n);
+
+ n->rx_pkt_cnt = 0;
+ virtio_notify(vdev, n->vqs[0].rx_vq);
+}
+
static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
{
VirtIONet *n = VIRTIO_NET(vdev);
@@ -1081,6 +1090,29 @@ static int virtio_net_handle_offloads(VirtIONet *n, uint8_t cmd,
}
}
+static int virtio_net_handle_coal(VirtIONet *n, uint8_t cmd,
+ struct iovec *iov, unsigned int iov_cnt)
+{
+ struct virtio_net_ctrl_coal coal;
+ size_t s;
+
+ s = iov_to_buf(iov, iov_cnt, 0, &coal, sizeof(coal));
+ if (s != sizeof(coal)) {
+ return VIRTIO_NET_ERR;
+ }
+
+ if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_RX_SET) {
+ n->rx_coal_usecs = le32_to_cpu(coal.max_usecs);
+ n->rx_coal_packets = le32_to_cpu(coal.max_packets);
+ } else if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_TX_SET) {
+ n->tx_coal_usecs = le32_to_cpu(coal.max_usecs);
+ n->tx_coal_packets = le32_to_cpu(coal.max_packets);
+ n->tx_timeout = n->tx_coal_usecs * 1000;
+ }
+
+ return VIRTIO_NET_OK;
+}
+
static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
struct iovec *iov, unsigned int iov_cnt)
{
@@ -1582,6 +1614,8 @@ size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
status = virtio_net_handle_mq(n, ctrl.cmd, iov, out_num);
} else if (ctrl.class == VIRTIO_NET_CTRL_GUEST_OFFLOADS) {
status = virtio_net_handle_offloads(n, ctrl.cmd, iov, out_num);
+ } else if (ctrl.class == VIRTIO_NET_CTRL_NOTF_COAL) {
+ status = virtio_net_handle_coal(n, ctrl.cmd, iov, out_num);
}
s = iov_from_buf(in_sg, in_num, 0, &status, sizeof(status));
@@ -2041,7 +2075,18 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
}
virtqueue_flush(q->rx_vq, i);
- virtio_notify(vdev, q->rx_vq);
+
+ /* rx coalescing */
+ n->rx_pkt_cnt += i;
+ if (n->rx_coal_usecs == 0 || n->rx_pkt_cnt >= n->rx_coal_packets) {
+ timer_del(n->rx_index_timer);
+ virtio_net_rx_notify(n);
+ } else {
+ if (n->rx_pkt_cnt == i) {
+ timer_mod(n->rx_index_timer,
+ qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) + n->rx_coal_usecs);
+ }
+ }
return size;
@@ -2900,6 +2945,7 @@ static void virtio_net_tx_timer(void *opaque)
if (ret == -EBUSY || ret == -EINVAL) {
return;
}
+ n->tx_pkt_cnt -= ret;
/*
* If we flush a full burst of packets, assume there are
* more coming and immediately rearm
@@ -2919,6 +2965,7 @@ static void virtio_net_tx_timer(void *opaque)
ret = virtio_net_flush_tx(q);
if (ret > 0) {
virtio_queue_set_notification(q->tx_vq, 0);
+ n->tx_pkt_cnt -= ret;
q->tx_waiting = 1;
timer_mod(q->tx_timer,
qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
@@ -2974,27 +3021,45 @@ static void virtio_net_tx_bh(void *opaque)
}
}
-static void virtio_net_add_queue(VirtIONet *n, int index)
+static void virtio_net_handle_tx_dispatch(VirtIODevice *vdev, VirtQueue *vq)
{
- VirtIODevice *vdev = VIRTIO_DEVICE(n);
+ VirtIONet *n = VIRTIO_NET(vdev);
- n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
- virtio_net_handle_rx);
+ n->tx_pkt_cnt++;
+ bool use_timer = n->tx_timer_activate || n->tx_coal_usecs > 0 ||
+ n->tx_coal_packets > 0;
- if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
- n->vqs[index].tx_vq =
- virtio_add_queue(vdev, n->net_conf.tx_queue_size,
- virtio_net_handle_tx_timer);
- n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
- virtio_net_tx_timer,
- &n->vqs[index]);
+ if (use_timer && n->tx_pkt_cnt < n->tx_coal_packets) {
+ virtio_net_handle_tx_timer(vdev, vq);
} else {
- n->vqs[index].tx_vq =
- virtio_add_queue(vdev, n->net_conf.tx_queue_size,
- virtio_net_handle_tx_bh);
- n->vqs[index].tx_bh = qemu_bh_new_guarded(virtio_net_tx_bh, &n->vqs[index],
- &DEVICE(vdev)->mem_reentrancy_guard);
+ n->tx_pkt_cnt = 0;
+ virtio_net_handle_tx_bh(vdev, vq);
}
+}
+
+static void virtio_net_add_queue(VirtIONet *n, int index)
+{
+ VirtIODevice *vdev = VIRTIO_DEVICE(n);
+
+ n->vqs[index].rx_vq =
+ virtio_add_queue(vdev,
+ n->net_conf.rx_queue_size,
+ virtio_net_handle_rx);
+
+ n->vqs[index].tx_vq =
+ virtio_add_queue(vdev,
+ n->net_conf.tx_queue_size,
+ virtio_net_handle_tx_dispatch);
+
+ n->vqs[index].tx_timer =
+ timer_new_ns(QEMU_CLOCK_VIRTUAL,
+ virtio_net_tx_timer,
+ &n->vqs[index]);
+
+ n->vqs[index].tx_bh =
+ qemu_bh_new_guarded(virtio_net_tx_bh,
+ &n->vqs[index],
+ &DEVICE(vdev)->mem_reentrancy_guard);
n->vqs[index].tx_waiting = 0;
n->vqs[index].n = n;
@@ -3089,6 +3154,7 @@ static void virtio_net_get_features(VirtIODevice *vdev, uint64_t *features,
virtio_features_or(features, features, n->host_features_ex);
virtio_add_feature_ex(features, VIRTIO_NET_F_MAC);
+ virtio_add_feature_ex(features, VIRTIO_NET_F_NOTF_COAL);
if (!peer_has_vnet_hdr(n)) {
virtio_clear_feature_ex(features, VIRTIO_NET_F_CSUM);
@@ -3972,6 +4038,10 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
error_printf("Defaulting to \"bh\"");
}
+ if (n->net_conf.tx && strcmp(n->net_conf.tx, "timer")) {
+ n->tx_timer_activate = true;
+ }
+
n->net_conf.tx_queue_size = MIN(virtio_net_max_tx_queue_size(n),
n->net_conf.tx_queue_size);
@@ -4048,6 +4118,14 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
n->rss_data.specified_hash_types.on_bits |
n->rss_data.specified_hash_types.auto_bits;
}
+ n->rx_pkt_cnt = 0;
+ n->tx_pkt_cnt = 0;
+ n->rx_coal_usecs = 0;
+ n->tx_coal_usecs = 0;
+ n->rx_coal_packets = 0;
+ n->tx_coal_packets = 0;
+ n->rx_index_timer = timer_new_us(QEMU_CLOCK_VIRTUAL,
+ virtio_net_rx_notify, n);
}
static void virtio_net_device_unrealize(DeviceState *dev)
@@ -4262,6 +4340,8 @@ static const Property virtio_net_properties[] = {
VIRTIO_NET_F_GUEST_USO6, true),
DEFINE_PROP_BIT64("host_uso", VirtIONet, host_features,
VIRTIO_NET_F_HOST_USO, true),
+ DEFINE_PROP_BIT64("vq_notf_coal", VirtIONet, host_features,
+ VIRTIO_NET_F_NOTF_COAL, true),
DEFINE_PROP_ON_OFF_AUTO_BIT64("hash-ipv4", VirtIONet,
rss_data.specified_hash_types,
VIRTIO_NET_HASH_REPORT_IPv4 - 1,
diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
index 6242aeb69c..104ed0ce8f 100644
--- a/hw/virtio/vhost-shadow-virtqueue.c
+++ b/hw/virtio/vhost-shadow-virtqueue.c
@@ -37,6 +37,7 @@ bool vhost_svq_valid_features(uint64_t features, Error **errp)
case VIRTIO_RING_F_INDIRECT_DESC:
continue;
+ case VIRTIO_F_RING_RESET:
case VIRTIO_F_ACCESS_PLATFORM:
/* SVQ trust in the host's IOMMU to translate addresses */
case VIRTIO_F_VERSION_1:
diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
index 2f8f11df86..8eb9bdb961 100644
--- a/hw/virtio/vhost-vdpa.c
+++ b/hw/virtio/vhost-vdpa.c
@@ -1541,6 +1541,9 @@ static int vhost_vdpa_get_features(struct vhost_dev *dev,
if (ret == 0) {
/* Add SVQ logging capabilities */
*features |= BIT_ULL(VHOST_F_LOG_ALL);
+
+ /* Add notification coalescing features */
+ *features |= BIT_ULL(VIRTIO_NET_F_NOTF_COAL);
}
return ret;
diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
index 5b8ab7bda7..024501ed37 100644
--- a/include/hw/virtio/virtio-net.h
+++ b/include/hw/virtio/virtio-net.h
@@ -231,6 +231,14 @@ struct VirtIONet {
struct EBPFRSSContext ebpf_rss;
uint32_t nr_ebpf_rss_fds;
char **ebpf_rss_fds;
+ QEMUTimer *rx_index_timer;
+ uint32_t rx_coal_usecs;
+ uint32_t rx_coal_packets;
+ uint32_t rx_pkt_cnt;
+ uint32_t tx_coal_usecs;
+ uint32_t tx_coal_packets;
+ uint32_t tx_pkt_cnt;
+ bool tx_timer_activate;
};
size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
index 3df6091274..6a5d0f4cae 100644
--- a/net/vhost-vdpa.c
+++ b/net/vhost-vdpa.c
@@ -61,6 +61,7 @@ static const int vdpa_feature_bits[] = {
VIRTIO_F_NOTIFY_ON_EMPTY,
VIRTIO_F_RING_PACKED,
VIRTIO_F_RING_RESET,
+ VIRTIO_F_ORDER_PLATFORM,
VIRTIO_F_VERSION_1,
VIRTIO_F_IN_ORDER,
VIRTIO_F_NOTIFICATION_DATA,
@@ -70,6 +71,8 @@ static const int vdpa_feature_bits[] = {
VIRTIO_NET_F_CTRL_RX,
VIRTIO_NET_F_CTRL_RX_EXTRA,
VIRTIO_NET_F_CTRL_VLAN,
+ VIRTIO_NET_F_GUEST_ANNOUNCE,
+ VIRTIO_NET_F_NOTF_COAL,
VIRTIO_NET_F_CTRL_VQ,
VIRTIO_NET_F_GSO,
VIRTIO_NET_F_GUEST_CSUM,
@@ -115,6 +118,13 @@ static const uint64_t vdpa_svq_device_features =
BIT_ULL(VIRTIO_NET_F_HOST_UFO) |
BIT_ULL(VIRTIO_NET_F_MRG_RXBUF) |
BIT_ULL(VIRTIO_NET_F_STATUS) |
+ BIT_ULL(VIRTIO_F_RING_RESET) |
+ BIT_ULL(VIRTIO_F_ORDER_PLATFORM) |
+ BIT_ULL(VIRTIO_NET_F_GUEST_USO4) |
+ BIT_ULL(VIRTIO_NET_F_GUEST_USO6) |
+ BIT_ULL(VIRTIO_NET_F_HOST_USO) |
+ BIT_ULL(VIRTIO_NET_F_GUEST_ANNOUNCE) |
+ BIT_ULL(VIRTIO_NET_F_NOTF_COAL) |
BIT_ULL(VIRTIO_NET_F_CTRL_VQ) |
BIT_ULL(VIRTIO_NET_F_GSO) |
BIT_ULL(VIRTIO_NET_F_CTRL_RX) |
--
2.53.0
^ permalink raw reply related [flat|nested] 4+ messages in thread
* Re: [PATCH v2] hw/net/virtio-net: add support for notification coalescing
2026-03-11 13:28 [PATCH v2] hw/net/virtio-net: add support for notification coalescing Koushik Dutta
@ 2026-03-12 10:17 ` Eugenio Perez Martin
2026-03-23 8:38 ` Koushik Dutta
0 siblings, 1 reply; 4+ messages in thread
From: Eugenio Perez Martin @ 2026-03-12 10:17 UTC (permalink / raw)
To: Koushik Dutta
Cc: qemu-devel, Stefano Garzarella, Michael S. Tsirkin, Jason Wang
On Wed, Mar 11, 2026 at 2:28 PM Koushik Dutta <kdutta@redhat.com> wrote:
>
> Implement VirtIO Network Notification Coalescing (Bit 53).
> This allows the guest to manage interrupt frequency using ethtool
> -C for both RX and TX paths.
>
> - Added VIRTIO_NET_F_NOTF_COAL to host features.
> - Implemented VIRTIO_NET_CTRL_NOTF_COAL class handling in
> virtio_net_handle_ctrl_iov.
> - Added logic to store and apply rx/tx usecs and max_packets.
> - Added packet counters and threshold logic for both RX and TX data paths.
> - Dynamic Dispatcher: Implemented a dispatcher mechanism that
> dynamically switches/activates the notification callback logic
> only after the guest enables TX coalescing via ethtool.
>
> This reduces interrupt overhead by batching notifications based on
> either a packet count or a time-based threshold.
>
> Signed-off-by: Koushik Dutta <kdutta@redhat.com>
> ---
> hw/net/virtio-net.c | 114 ++++++++++++++++++++++++-----
> hw/virtio/vhost-shadow-virtqueue.c | 1 +
> hw/virtio/vhost-vdpa.c | 3 +
> include/hw/virtio/virtio-net.h | 8 ++
> net/vhost-vdpa.c | 10 +++
> 5 files changed, 119 insertions(+), 17 deletions(-)
>
> diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> index eccb48ad42..96aa70aea8 100644
> --- a/hw/net/virtio-net.c
> +++ b/hw/net/virtio-net.c
> @@ -157,6 +157,15 @@ static void flush_or_purge_queued_packets(NetClientState *nc)
> * - we could suppress RX interrupt if we were so inclined.
> */
>
> +static void virtio_net_rx_notify(void *opaque)
> +{
> + VirtIONet *n = opaque;
> + VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +
> + n->rx_pkt_cnt = 0;
> + virtio_notify(vdev, n->vqs[0].rx_vq);
> +}
> +
> static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
> {
> VirtIONet *n = VIRTIO_NET(vdev);
> @@ -1081,6 +1090,29 @@ static int virtio_net_handle_offloads(VirtIONet *n, uint8_t cmd,
> }
> }
>
> +static int virtio_net_handle_coal(VirtIONet *n, uint8_t cmd,
> + struct iovec *iov, unsigned int iov_cnt)
> +{
> + struct virtio_net_ctrl_coal coal;
> + size_t s;
> +
> + s = iov_to_buf(iov, iov_cnt, 0, &coal, sizeof(coal));
> + if (s != sizeof(coal)) {
> + return VIRTIO_NET_ERR;
> + }
> +
> + if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_RX_SET) {
> + n->rx_coal_usecs = le32_to_cpu(coal.max_usecs);
> + n->rx_coal_packets = le32_to_cpu(coal.max_packets);
> + } else if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_TX_SET) {
> + n->tx_coal_usecs = le32_to_cpu(coal.max_usecs);
> + n->tx_coal_packets = le32_to_cpu(coal.max_packets);
> + n->tx_timeout = n->tx_coal_usecs * 1000;
> + }
> +
> + return VIRTIO_NET_OK;
> +}
> +
> static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
> struct iovec *iov, unsigned int iov_cnt)
> {
> @@ -1582,6 +1614,8 @@ size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
> status = virtio_net_handle_mq(n, ctrl.cmd, iov, out_num);
> } else if (ctrl.class == VIRTIO_NET_CTRL_GUEST_OFFLOADS) {
> status = virtio_net_handle_offloads(n, ctrl.cmd, iov, out_num);
> + } else if (ctrl.class == VIRTIO_NET_CTRL_NOTF_COAL) {
> + status = virtio_net_handle_coal(n, ctrl.cmd, iov, out_num);
> }
>
> s = iov_from_buf(in_sg, in_num, 0, &status, sizeof(status));
> @@ -2041,7 +2075,18 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
> }
>
> virtqueue_flush(q->rx_vq, i);
> - virtio_notify(vdev, q->rx_vq);
> +
> + /* rx coalescing */
> + n->rx_pkt_cnt += i;
> + if (n->rx_coal_usecs == 0 || n->rx_pkt_cnt >= n->rx_coal_packets) {
> + timer_del(n->rx_index_timer);
> + virtio_net_rx_notify(n);
> + } else {
> + if (n->rx_pkt_cnt == i) {
Maybe it's better to check if !timer_pending? It wasn't immediately
clear to me that `n->rx_pkt_cnt == i` until I realized that
`n->rx_pkt_cnt` is 0 at the beginning of the function for that
condition to be true.
> + timer_mod(n->rx_index_timer,
> + qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) + n->rx_coal_usecs);
> + }
> + }
>
> return size;
>
> @@ -2900,6 +2945,7 @@ static void virtio_net_tx_timer(void *opaque)
> if (ret == -EBUSY || ret == -EINVAL) {
> return;
> }
> + n->tx_pkt_cnt -= ret;
> /*
> * If we flush a full burst of packets, assume there are
> * more coming and immediately rearm
> @@ -2919,6 +2965,7 @@ static void virtio_net_tx_timer(void *opaque)
> ret = virtio_net_flush_tx(q);
> if (ret > 0) {
> virtio_queue_set_notification(q->tx_vq, 0);
> + n->tx_pkt_cnt -= ret;
If we got his way, we must control for underflow here.
But I think it should be n->pt_pkt_cnt = 0, isn't it?
> q->tx_waiting = 1;
> timer_mod(q->tx_timer,
> qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);
> @@ -2974,27 +3021,45 @@ static void virtio_net_tx_bh(void *opaque)
> }
> }
>
> -static void virtio_net_add_queue(VirtIONet *n, int index)
> +static void virtio_net_handle_tx_dispatch(VirtIODevice *vdev, VirtQueue *vq)
> {
> - VirtIODevice *vdev = VIRTIO_DEVICE(n);
> + VirtIONet *n = VIRTIO_NET(vdev);
>
> - n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,
> - virtio_net_handle_rx);
> + n->tx_pkt_cnt++;
> + bool use_timer = n->tx_timer_activate || n->tx_coal_usecs > 0 ||
> + n->tx_coal_packets > 0;
No declarations in the middle of the function.
Also, why use_timer = true as long as n->tx_coal_packets > 0?
>
> - if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> - n->vqs[index].tx_vq =
> - virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> - virtio_net_handle_tx_timer);
> - n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> - virtio_net_tx_timer,
> - &n->vqs[index]);
> + if (use_timer && n->tx_pkt_cnt < n->tx_coal_packets) {
> + virtio_net_handle_tx_timer(vdev, vq);
> } else {
> - n->vqs[index].tx_vq =
> - virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> - virtio_net_handle_tx_bh);
> - n->vqs[index].tx_bh = qemu_bh_new_guarded(virtio_net_tx_bh, &n->vqs[index],
> - &DEVICE(vdev)->mem_reentrancy_guard);
> + n->tx_pkt_cnt = 0;
> + virtio_net_handle_tx_bh(vdev, vq);
> }
> +}
> +
> +static void virtio_net_add_queue(VirtIONet *n, int index)
> +{
> + VirtIODevice *vdev = VIRTIO_DEVICE(n);
> +
> + n->vqs[index].rx_vq =
> + virtio_add_queue(vdev,
> + n->net_conf.rx_queue_size,
> + virtio_net_handle_rx);
> +
> + n->vqs[index].tx_vq =
> + virtio_add_queue(vdev,
> + n->net_conf.tx_queue_size,
> + virtio_net_handle_tx_dispatch);
> +
> + n->vqs[index].tx_timer =
> + timer_new_ns(QEMU_CLOCK_VIRTUAL,
> + virtio_net_tx_timer,
> + &n->vqs[index]);
We should avoid creating a new timer if it will not be used by
default. Create it only if cmdline enables it or the guest enable it
via control vq.
> +
> + n->vqs[index].tx_bh =
> + qemu_bh_new_guarded(virtio_net_tx_bh,
> + &n->vqs[index],
> + &DEVICE(vdev)->mem_reentrancy_guard);
>
> n->vqs[index].tx_waiting = 0;
> n->vqs[index].n = n;
> @@ -3089,6 +3154,7 @@ static void virtio_net_get_features(VirtIODevice *vdev, uint64_t *features,
> virtio_features_or(features, features, n->host_features_ex);
>
> virtio_add_feature_ex(features, VIRTIO_NET_F_MAC);
> + virtio_add_feature_ex(features, VIRTIO_NET_F_NOTF_COAL);
We shouldn't enable VIRTIO_NET_F_NOTF_COAL unconditionally, it should
be regulated by the cmdline property.
>
> if (!peer_has_vnet_hdr(n)) {
> virtio_clear_feature_ex(features, VIRTIO_NET_F_CSUM);
> @@ -3972,6 +4038,10 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
> error_printf("Defaulting to \"bh\"");
> }
>
> + if (n->net_conf.tx && strcmp(n->net_conf.tx, "timer")) {
> + n->tx_timer_activate = true;
> + }
> +
> n->net_conf.tx_queue_size = MIN(virtio_net_max_tx_queue_size(n),
> n->net_conf.tx_queue_size);
>
> @@ -4048,6 +4118,14 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)
> n->rss_data.specified_hash_types.on_bits |
> n->rss_data.specified_hash_types.auto_bits;
> }
> + n->rx_pkt_cnt = 0;
> + n->tx_pkt_cnt = 0;
> + n->rx_coal_usecs = 0;
> + n->tx_coal_usecs = 0;
> + n->rx_coal_packets = 0;
> + n->tx_coal_packets = 0;
> + n->rx_index_timer = timer_new_us(QEMU_CLOCK_VIRTUAL,
> + virtio_net_rx_notify, n);
Same as the tx timer. Is it worth creating a new timer even if it will
not be used by default?
> }
>
> static void virtio_net_device_unrealize(DeviceState *dev)
> @@ -4262,6 +4340,8 @@ static const Property virtio_net_properties[] = {
> VIRTIO_NET_F_GUEST_USO6, true),
> DEFINE_PROP_BIT64("host_uso", VirtIONet, host_features,
> VIRTIO_NET_F_HOST_USO, true),
> + DEFINE_PROP_BIT64("vq_notf_coal", VirtIONet, host_features,
> + VIRTIO_NET_F_NOTF_COAL, true),
> DEFINE_PROP_ON_OFF_AUTO_BIT64("hash-ipv4", VirtIONet,
> rss_data.specified_hash_types,
> VIRTIO_NET_HASH_REPORT_IPv4 - 1,
> diff --git a/hw/virtio/vhost-shadow-virtqueue.c b/hw/virtio/vhost-shadow-virtqueue.c
> index 6242aeb69c..104ed0ce8f 100644
> --- a/hw/virtio/vhost-shadow-virtqueue.c
> +++ b/hw/virtio/vhost-shadow-virtqueue.c
> @@ -37,6 +37,7 @@ bool vhost_svq_valid_features(uint64_t features, Error **errp)
> case VIRTIO_RING_F_INDIRECT_DESC:
> continue;
>
> + case VIRTIO_F_RING_RESET:
This patch does not handle VIRTIO_F_RING_RESET, so this should not be enabled.
> case VIRTIO_F_ACCESS_PLATFORM:
> /* SVQ trust in the host's IOMMU to translate addresses */
> case VIRTIO_F_VERSION_1:
> diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> index 2f8f11df86..8eb9bdb961 100644
> --- a/hw/virtio/vhost-vdpa.c
> +++ b/hw/virtio/vhost-vdpa.c
> @@ -1541,6 +1541,9 @@ static int vhost_vdpa_get_features(struct vhost_dev *dev,
> if (ret == 0) {
> /* Add SVQ logging capabilities */
> *features |= BIT_ULL(VHOST_F_LOG_ALL);
> +
> + /* Add notification coalescing features */
> + *features |= BIT_ULL(VIRTIO_NET_F_NOTF_COAL);
> }
>
> return ret;
> diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h
> index 5b8ab7bda7..024501ed37 100644
> --- a/include/hw/virtio/virtio-net.h
> +++ b/include/hw/virtio/virtio-net.h
> @@ -231,6 +231,14 @@ struct VirtIONet {
> struct EBPFRSSContext ebpf_rss;
> uint32_t nr_ebpf_rss_fds;
> char **ebpf_rss_fds;
> + QEMUTimer *rx_index_timer;
> + uint32_t rx_coal_usecs;
> + uint32_t rx_coal_packets;
> + uint32_t rx_pkt_cnt;
> + uint32_t tx_coal_usecs;
> + uint32_t tx_coal_packets;
> + uint32_t tx_pkt_cnt;
> + bool tx_timer_activate;
> };
>
> size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
> diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> index 3df6091274..6a5d0f4cae 100644
> --- a/net/vhost-vdpa.c
> +++ b/net/vhost-vdpa.c
> @@ -61,6 +61,7 @@ static const int vdpa_feature_bits[] = {
> VIRTIO_F_NOTIFY_ON_EMPTY,
> VIRTIO_F_RING_PACKED,
> VIRTIO_F_RING_RESET,
> + VIRTIO_F_ORDER_PLATFORM,
> VIRTIO_F_VERSION_1,
> VIRTIO_F_IN_ORDER,
> VIRTIO_F_NOTIFICATION_DATA,
> @@ -70,6 +71,8 @@ static const int vdpa_feature_bits[] = {
> VIRTIO_NET_F_CTRL_RX,
> VIRTIO_NET_F_CTRL_RX_EXTRA,
> VIRTIO_NET_F_CTRL_VLAN,
> + VIRTIO_NET_F_GUEST_ANNOUNCE,
> + VIRTIO_NET_F_NOTF_COAL,
Only this feature can be added to vdpa_feature_bits. The rest of them
must not be added to any other array.
> VIRTIO_NET_F_CTRL_VQ,
> VIRTIO_NET_F_GSO,
> VIRTIO_NET_F_GUEST_CSUM,
> @@ -115,6 +118,13 @@ static const uint64_t vdpa_svq_device_features =
> BIT_ULL(VIRTIO_NET_F_HOST_UFO) |
> BIT_ULL(VIRTIO_NET_F_MRG_RXBUF) |
> BIT_ULL(VIRTIO_NET_F_STATUS) |
> + BIT_ULL(VIRTIO_F_RING_RESET) |
> + BIT_ULL(VIRTIO_F_ORDER_PLATFORM) |
> + BIT_ULL(VIRTIO_NET_F_GUEST_USO4) |
> + BIT_ULL(VIRTIO_NET_F_GUEST_USO6) |
> + BIT_ULL(VIRTIO_NET_F_HOST_USO) |
> + BIT_ULL(VIRTIO_NET_F_GUEST_ANNOUNCE) |
> + BIT_ULL(VIRTIO_NET_F_NOTF_COAL) |
> BIT_ULL(VIRTIO_NET_F_CTRL_VQ) |
> BIT_ULL(VIRTIO_NET_F_GSO) |
> BIT_ULL(VIRTIO_NET_F_CTRL_RX) |
> --
> 2.53.0
>
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] hw/net/virtio-net: add support for notification coalescing
2026-03-12 10:17 ` Eugenio Perez Martin
@ 2026-03-23 8:38 ` Koushik Dutta
2026-03-23 9:46 ` Eugenio Perez Martin
0 siblings, 1 reply; 4+ messages in thread
From: Koushik Dutta @ 2026-03-23 8:38 UTC (permalink / raw)
To: Eugenio Perez Martin
Cc: qemu-devel, Stefano Garzarella, Michael S. Tsirkin, Jason Wang
[-- Attachment #1: Type: text/plain, Size: 15557 bytes --]
Hi Eugenio,
Regarding the point about not enabling VIRTIO_NET_F_NOTF_COAL
unconditionally: since feature negotiation happens during VM bootup and
coalescing is configured via ethtool after the VM has already booted, how
would we handle this under a conditional property?
If the feature isn't negotiated at the start, we wouldn't be able to enable
it dynamically later. Could you clarify how you'd like the command-line
regulation to interact with the guest's ability to enable it later?
------------------------------------------------------------
> @@ -37,6 +37,7 @@ bool vhost_svq_valid_features(uint64_t features, Error
**errp)
> case VIRTIO_RING_F_INDIRECT_DESC:
> continue;
>
> + case VIRTIO_F_RING_RESET:
This patch does not handle VIRTIO_F_RING_RESET, so this should not be
enabled.
=> I included VIRTIO_F_RING_RESET in the valid features list because the
vDPA host device offers it by default; without it, SVQ fails the feature
negotiation check during initialization.
qemu-system-x86_64: -netdev
type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-svq=on: SVQ
Invalid device feature flags, offer: 0x1e0010330bfffa7, ok:
0x1e0000330bfffa7
Regards,
Koushik Dutta
On Thu, Mar 12, 2026 at 3:47 PM Eugenio Perez Martin <eperezma@redhat.com>
wrote:
> On Wed, Mar 11, 2026 at 2:28 PM Koushik Dutta <kdutta@redhat.com> wrote:
> >
> > Implement VirtIO Network Notification Coalescing (Bit 53).
> > This allows the guest to manage interrupt frequency using ethtool
> > -C for both RX and TX paths.
> >
> > - Added VIRTIO_NET_F_NOTF_COAL to host features.
> > - Implemented VIRTIO_NET_CTRL_NOTF_COAL class handling in
> > virtio_net_handle_ctrl_iov.
> > - Added logic to store and apply rx/tx usecs and max_packets.
> > - Added packet counters and threshold logic for both RX and TX data
> paths.
> > - Dynamic Dispatcher: Implemented a dispatcher mechanism that
> > dynamically switches/activates the notification callback logic
> > only after the guest enables TX coalescing via ethtool.
> >
> > This reduces interrupt overhead by batching notifications based on
> > either a packet count or a time-based threshold.
> >
> > Signed-off-by: Koushik Dutta <kdutta@redhat.com>
> > ---
> > hw/net/virtio-net.c | 114 ++++++++++++++++++++++++-----
> > hw/virtio/vhost-shadow-virtqueue.c | 1 +
> > hw/virtio/vhost-vdpa.c | 3 +
> > include/hw/virtio/virtio-net.h | 8 ++
> > net/vhost-vdpa.c | 10 +++
> > 5 files changed, 119 insertions(+), 17 deletions(-)
> >
> > diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c
> > index eccb48ad42..96aa70aea8 100644
> > --- a/hw/net/virtio-net.c
> > +++ b/hw/net/virtio-net.c
> > @@ -157,6 +157,15 @@ static void
> flush_or_purge_queued_packets(NetClientState *nc)
> > * - we could suppress RX interrupt if we were so inclined.
> > */
> >
> > +static void virtio_net_rx_notify(void *opaque)
> > +{
> > + VirtIONet *n = opaque;
> > + VirtIODevice *vdev = VIRTIO_DEVICE(n);
> > +
> > + n->rx_pkt_cnt = 0;
> > + virtio_notify(vdev, n->vqs[0].rx_vq);
> > +}
> > +
> > static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)
> > {
> > VirtIONet *n = VIRTIO_NET(vdev);
> > @@ -1081,6 +1090,29 @@ static int virtio_net_handle_offloads(VirtIONet
> *n, uint8_t cmd,
> > }
> > }
> >
> > +static int virtio_net_handle_coal(VirtIONet *n, uint8_t cmd,
> > + struct iovec *iov, unsigned int
> iov_cnt)
> > +{
> > + struct virtio_net_ctrl_coal coal;
> > + size_t s;
> > +
> > + s = iov_to_buf(iov, iov_cnt, 0, &coal, sizeof(coal));
> > + if (s != sizeof(coal)) {
> > + return VIRTIO_NET_ERR;
> > + }
> > +
> > + if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_RX_SET) {
> > + n->rx_coal_usecs = le32_to_cpu(coal.max_usecs);
> > + n->rx_coal_packets = le32_to_cpu(coal.max_packets);
> > + } else if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_TX_SET) {
> > + n->tx_coal_usecs = le32_to_cpu(coal.max_usecs);
> > + n->tx_coal_packets = le32_to_cpu(coal.max_packets);
> > + n->tx_timeout = n->tx_coal_usecs * 1000;
> > + }
> > +
> > + return VIRTIO_NET_OK;
> > +}
> > +
> > static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,
> > struct iovec *iov, unsigned int
> iov_cnt)
> > {
> > @@ -1582,6 +1614,8 @@ size_t virtio_net_handle_ctrl_iov(VirtIODevice
> *vdev,
> > status = virtio_net_handle_mq(n, ctrl.cmd, iov, out_num);
> > } else if (ctrl.class == VIRTIO_NET_CTRL_GUEST_OFFLOADS) {
> > status = virtio_net_handle_offloads(n, ctrl.cmd, iov, out_num);
> > + } else if (ctrl.class == VIRTIO_NET_CTRL_NOTF_COAL) {
> > + status = virtio_net_handle_coal(n, ctrl.cmd, iov, out_num);
> > }
> >
> > s = iov_from_buf(in_sg, in_num, 0, &status, sizeof(status));
> > @@ -2041,7 +2075,18 @@ static ssize_t
> virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,
> > }
> >
> > virtqueue_flush(q->rx_vq, i);
> > - virtio_notify(vdev, q->rx_vq);
> > +
> > + /* rx coalescing */
> > + n->rx_pkt_cnt += i;
> > + if (n->rx_coal_usecs == 0 || n->rx_pkt_cnt >= n->rx_coal_packets) {
> > + timer_del(n->rx_index_timer);
> > + virtio_net_rx_notify(n);
> > + } else {
> > + if (n->rx_pkt_cnt == i) {
>
> Maybe it's better to check if !timer_pending? It wasn't immediately
> clear to me that `n->rx_pkt_cnt == i` until I realized that
> `n->rx_pkt_cnt` is 0 at the beginning of the function for that
> condition to be true.
>
> > + timer_mod(n->rx_index_timer,
> > + qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) +
> n->rx_coal_usecs);
> > + }
> > + }
> >
> > return size;
> >
> > @@ -2900,6 +2945,7 @@ static void virtio_net_tx_timer(void *opaque)
> > if (ret == -EBUSY || ret == -EINVAL) {
> > return;
> > }
> > + n->tx_pkt_cnt -= ret;
> > /*
> > * If we flush a full burst of packets, assume there are
> > * more coming and immediately rearm
> > @@ -2919,6 +2965,7 @@ static void virtio_net_tx_timer(void *opaque)
> > ret = virtio_net_flush_tx(q);
> > if (ret > 0) {
> > virtio_queue_set_notification(q->tx_vq, 0);
> > + n->tx_pkt_cnt -= ret;
>
> If we got his way, we must control for underflow here.
>
> But I think it should be n->pt_pkt_cnt = 0, isn't it?
>
> > q->tx_waiting = 1;
> > timer_mod(q->tx_timer,
> > qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) +
> n->tx_timeout);
> > @@ -2974,27 +3021,45 @@ static void virtio_net_tx_bh(void *opaque)
> > }
> > }
> >
> > -static void virtio_net_add_queue(VirtIONet *n, int index)
> > +static void virtio_net_handle_tx_dispatch(VirtIODevice *vdev, VirtQueue
> *vq)
> > {
> > - VirtIODevice *vdev = VIRTIO_DEVICE(n);
> > + VirtIONet *n = VIRTIO_NET(vdev);
> >
> > - n->vqs[index].rx_vq = virtio_add_queue(vdev,
> n->net_conf.rx_queue_size,
> > - virtio_net_handle_rx);
> > + n->tx_pkt_cnt++;
> > + bool use_timer = n->tx_timer_activate || n->tx_coal_usecs > 0 ||
> > + n->tx_coal_packets > 0;
>
> No declarations in the middle of the function.
>
> Also, why use_timer = true as long as n->tx_coal_packets > 0?
>
> >
> > - if (n->net_conf.tx && !strcmp(n->net_conf.tx, "timer")) {
> > - n->vqs[index].tx_vq =
> > - virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> > - virtio_net_handle_tx_timer);
> > - n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
> > - virtio_net_tx_timer,
> > - &n->vqs[index]);
> > + if (use_timer && n->tx_pkt_cnt < n->tx_coal_packets) {
> > + virtio_net_handle_tx_timer(vdev, vq);
> > } else {
> > - n->vqs[index].tx_vq =
> > - virtio_add_queue(vdev, n->net_conf.tx_queue_size,
> > - virtio_net_handle_tx_bh);
> > - n->vqs[index].tx_bh = qemu_bh_new_guarded(virtio_net_tx_bh,
> &n->vqs[index],
> > -
> &DEVICE(vdev)->mem_reentrancy_guard);
> > + n->tx_pkt_cnt = 0;
> > + virtio_net_handle_tx_bh(vdev, vq);
> > }
> > +}
> > +
> > +static void virtio_net_add_queue(VirtIONet *n, int index)
> > +{
> > + VirtIODevice *vdev = VIRTIO_DEVICE(n);
> > +
> > + n->vqs[index].rx_vq =
> > + virtio_add_queue(vdev,
> > + n->net_conf.rx_queue_size,
> > + virtio_net_handle_rx);
> > +
> > + n->vqs[index].tx_vq =
> > + virtio_add_queue(vdev,
> > + n->net_conf.tx_queue_size,
> > + virtio_net_handle_tx_dispatch);
> > +
> > + n->vqs[index].tx_timer =
> > + timer_new_ns(QEMU_CLOCK_VIRTUAL,
> > + virtio_net_tx_timer,
> > + &n->vqs[index]);
>
> We should avoid creating a new timer if it will not be used by
> default. Create it only if cmdline enables it or the guest enable it
> via control vq.
>
> > +
> > + n->vqs[index].tx_bh =
> > + qemu_bh_new_guarded(virtio_net_tx_bh,
> > + &n->vqs[index],
> > + &DEVICE(vdev)->mem_reentrancy_guard);
> >
> > n->vqs[index].tx_waiting = 0;
> > n->vqs[index].n = n;
> > @@ -3089,6 +3154,7 @@ static void virtio_net_get_features(VirtIODevice
> *vdev, uint64_t *features,
> > virtio_features_or(features, features, n->host_features_ex);
> >
> > virtio_add_feature_ex(features, VIRTIO_NET_F_MAC);
> > + virtio_add_feature_ex(features, VIRTIO_NET_F_NOTF_COAL);
>
> We shouldn't enable VIRTIO_NET_F_NOTF_COAL unconditionally, it should
> be regulated by the cmdline property.
>
> >
> > if (!peer_has_vnet_hdr(n)) {
> > virtio_clear_feature_ex(features, VIRTIO_NET_F_CSUM);
> > @@ -3972,6 +4038,10 @@ static void virtio_net_device_realize(DeviceState
> *dev, Error **errp)
> > error_printf("Defaulting to \"bh\"");
> > }
> >
> > + if (n->net_conf.tx && strcmp(n->net_conf.tx, "timer")) {
> > + n->tx_timer_activate = true;
> > + }
> > +
> > n->net_conf.tx_queue_size = MIN(virtio_net_max_tx_queue_size(n),
> > n->net_conf.tx_queue_size);
> >
> > @@ -4048,6 +4118,14 @@ static void virtio_net_device_realize(DeviceState
> *dev, Error **errp)
> > n->rss_data.specified_hash_types.on_bits |
> > n->rss_data.specified_hash_types.auto_bits;
> > }
> > + n->rx_pkt_cnt = 0;
> > + n->tx_pkt_cnt = 0;
> > + n->rx_coal_usecs = 0;
> > + n->tx_coal_usecs = 0;
> > + n->rx_coal_packets = 0;
> > + n->tx_coal_packets = 0;
> > + n->rx_index_timer = timer_new_us(QEMU_CLOCK_VIRTUAL,
> > + virtio_net_rx_notify, n);
>
> Same as the tx timer. Is it worth creating a new timer even if it will
> not be used by default?
>
> > }
> >
> > static void virtio_net_device_unrealize(DeviceState *dev)
> > @@ -4262,6 +4340,8 @@ static const Property virtio_net_properties[] = {
> > VIRTIO_NET_F_GUEST_USO6, true),
> > DEFINE_PROP_BIT64("host_uso", VirtIONet, host_features,
> > VIRTIO_NET_F_HOST_USO, true),
> > + DEFINE_PROP_BIT64("vq_notf_coal", VirtIONet, host_features,
> > + VIRTIO_NET_F_NOTF_COAL, true),
> > DEFINE_PROP_ON_OFF_AUTO_BIT64("hash-ipv4", VirtIONet,
> > rss_data.specified_hash_types,
> > VIRTIO_NET_HASH_REPORT_IPv4 - 1,
> > diff --git a/hw/virtio/vhost-shadow-virtqueue.c
> b/hw/virtio/vhost-shadow-virtqueue.c
> > index 6242aeb69c..104ed0ce8f 100644
> > --- a/hw/virtio/vhost-shadow-virtqueue.c
> > +++ b/hw/virtio/vhost-shadow-virtqueue.c
> > @@ -37,6 +37,7 @@ bool vhost_svq_valid_features(uint64_t features, Error
> **errp)
> > case VIRTIO_RING_F_INDIRECT_DESC:
> > continue;
> >
> > + case VIRTIO_F_RING_RESET:
>
> This patch does not handle VIRTIO_F_RING_RESET, so this should not be
> enabled.
>
> > case VIRTIO_F_ACCESS_PLATFORM:
> > /* SVQ trust in the host's IOMMU to translate addresses */
> > case VIRTIO_F_VERSION_1:
> > diff --git a/hw/virtio/vhost-vdpa.c b/hw/virtio/vhost-vdpa.c
> > index 2f8f11df86..8eb9bdb961 100644
> > --- a/hw/virtio/vhost-vdpa.c
> > +++ b/hw/virtio/vhost-vdpa.c
> > @@ -1541,6 +1541,9 @@ static int vhost_vdpa_get_features(struct
> vhost_dev *dev,
> > if (ret == 0) {
> > /* Add SVQ logging capabilities */
> > *features |= BIT_ULL(VHOST_F_LOG_ALL);
> > +
> > + /* Add notification coalescing features */
> > + *features |= BIT_ULL(VIRTIO_NET_F_NOTF_COAL);
> > }
> >
> > return ret;
> > diff --git a/include/hw/virtio/virtio-net.h
> b/include/hw/virtio/virtio-net.h
> > index 5b8ab7bda7..024501ed37 100644
> > --- a/include/hw/virtio/virtio-net.h
> > +++ b/include/hw/virtio/virtio-net.h
> > @@ -231,6 +231,14 @@ struct VirtIONet {
> > struct EBPFRSSContext ebpf_rss;
> > uint32_t nr_ebpf_rss_fds;
> > char **ebpf_rss_fds;
> > + QEMUTimer *rx_index_timer;
> > + uint32_t rx_coal_usecs;
> > + uint32_t rx_coal_packets;
> > + uint32_t rx_pkt_cnt;
> > + uint32_t tx_coal_usecs;
> > + uint32_t tx_coal_packets;
> > + uint32_t tx_pkt_cnt;
> > + bool tx_timer_activate;
> > };
> >
> > size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,
> > diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c
> > index 3df6091274..6a5d0f4cae 100644
> > --- a/net/vhost-vdpa.c
> > +++ b/net/vhost-vdpa.c
> > @@ -61,6 +61,7 @@ static const int vdpa_feature_bits[] = {
> > VIRTIO_F_NOTIFY_ON_EMPTY,
> > VIRTIO_F_RING_PACKED,
> > VIRTIO_F_RING_RESET,
> > + VIRTIO_F_ORDER_PLATFORM,
> > VIRTIO_F_VERSION_1,
> > VIRTIO_F_IN_ORDER,
> > VIRTIO_F_NOTIFICATION_DATA,
> > @@ -70,6 +71,8 @@ static const int vdpa_feature_bits[] = {
> > VIRTIO_NET_F_CTRL_RX,
> > VIRTIO_NET_F_CTRL_RX_EXTRA,
> > VIRTIO_NET_F_CTRL_VLAN,
> > + VIRTIO_NET_F_GUEST_ANNOUNCE,
> > + VIRTIO_NET_F_NOTF_COAL,
>
> Only this feature can be added to vdpa_feature_bits. The rest of them
> must not be added to any other array.
>
> > VIRTIO_NET_F_CTRL_VQ,
> > VIRTIO_NET_F_GSO,
> > VIRTIO_NET_F_GUEST_CSUM,
> > @@ -115,6 +118,13 @@ static const uint64_t vdpa_svq_device_features =
> > BIT_ULL(VIRTIO_NET_F_HOST_UFO) |
> > BIT_ULL(VIRTIO_NET_F_MRG_RXBUF) |
> > BIT_ULL(VIRTIO_NET_F_STATUS) |
> > + BIT_ULL(VIRTIO_F_RING_RESET) |
> > + BIT_ULL(VIRTIO_F_ORDER_PLATFORM) |
> > + BIT_ULL(VIRTIO_NET_F_GUEST_USO4) |
> > + BIT_ULL(VIRTIO_NET_F_GUEST_USO6) |
> > + BIT_ULL(VIRTIO_NET_F_HOST_USO) |
> > + BIT_ULL(VIRTIO_NET_F_GUEST_ANNOUNCE) |
> > + BIT_ULL(VIRTIO_NET_F_NOTF_COAL) |
> > BIT_ULL(VIRTIO_NET_F_CTRL_VQ) |
> > BIT_ULL(VIRTIO_NET_F_GSO) |
> > BIT_ULL(VIRTIO_NET_F_CTRL_RX) |
> > --
> > 2.53.0
> >
>
>
[-- Attachment #2: Type: text/html, Size: 19153 bytes --]
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH v2] hw/net/virtio-net: add support for notification coalescing
2026-03-23 8:38 ` Koushik Dutta
@ 2026-03-23 9:46 ` Eugenio Perez Martin
0 siblings, 0 replies; 4+ messages in thread
From: Eugenio Perez Martin @ 2026-03-23 9:46 UTC (permalink / raw)
To: Koushik Dutta
Cc: qemu-devel, Stefano Garzarella, Michael S. Tsirkin, Jason Wang
On Mon, Mar 23, 2026 at 9:39 AM Koushik Dutta <kdutta@redhat.com> wrote:
>
> Hi Eugenio,
> Regarding the point about not enabling VIRTIO_NET_F_NOTF_COAL unconditionally: since feature negotiation happens during VM bootup and coalescing is configured via ethtool after the VM has already booted, how would we handle this under a conditional property?
>
> If the feature isn't negotiated at the start, we wouldn't be able to enable it dynamically later. Could you clarify how you'd like the command-line regulation to interact with the guest's ability to enable it later?
Replying at the position of the comment, marked with [1]. Please
interleave your reply for the next time, as it makes revision easier
:) [2].
> ------------------------------------------------------------
>
> > @@ -37,6 +37,7 @@ bool vhost_svq_valid_features(uint64_t features, Error **errp)
> > case VIRTIO_RING_F_INDIRECT_DESC:
> > continue;
> >
> > + case VIRTIO_F_RING_RESET:
>
> This patch does not handle VIRTIO_F_RING_RESET, so this should not be enabled.
>
> => I included VIRTIO_F_RING_RESET in the valid features list because the vDPA host device offers it by default; without it, SVQ fails the feature negotiation check during initialization.
> qemu-system-x86_64: -netdev type=vhost-vdpa,vhostdev=/dev/vhost-vdpa-0,id=vhost-vdpa0,x-svq=on: SVQ Invalid device feature flags, offer: 0x1e0010330bfffa7, ok: 0x1e0000330bfffa7
>
Since you're testing the feature with nested virtualization, you can
disable the features in the L0 QEMU with:
-device virtio-net-pci,...,queue_reset=off,iommu_platform=off,guest_uso4=off,guest_uso6=off,host_uso=off,guest_announce=off
> Regards,
> Koushik Dutta
>
> On Thu, Mar 12, 2026 at 3:47 PM Eugenio Perez Martin <eperezma@redhat.com> wrote:
>>
>> On Wed, Mar 11, 2026 at 2:28 PM Koushik Dutta <kdutta@redhat.com> wrote:
>> >
[...]
>> > +
>> > +static void virtio_net_add_queue(VirtIONet *n, int index)
>> > +{
>> > + VirtIODevice *vdev = VIRTIO_DEVICE(n);
>> > +
>> > + n->vqs[index].rx_vq =
>> > + virtio_add_queue(vdev,
>> > + n->net_conf.rx_queue_size,
>> > + virtio_net_handle_rx);
>> > +
>> > + n->vqs[index].tx_vq =
>> > + virtio_add_queue(vdev,
>> > + n->net_conf.tx_queue_size,
>> > + virtio_net_handle_tx_dispatch);
>> > +
>> > + n->vqs[index].tx_timer =
>> > + timer_new_ns(QEMU_CLOCK_VIRTUAL,
>> > + virtio_net_tx_timer,
>> > + &n->vqs[index]);
>>
>> We should avoid creating a new timer if it will not be used by
>> default. Create it only if cmdline enables it or the guest enable it
>> via control vq.
>>
[1]
I'm proposing we switch this to something like:
if (!strcmp(n->net_conf.tx, "timer")) {
n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
virtio_net_tx_timer, &n->vqs[index]);
}
And, in the CVQ code that you created,
if (n->tx_coal_usecs) {
n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,
virtio_net_tx_timer, &n->vqs[index]);
}
And the same applies to RX timers.
[2] https://subspace.kernel.org/etiquette.html#do-not-top-post-when-replying
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-03-23 9:47 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz follow: Atom feed
-- links below jump to the message on this page --
2026-03-11 13:28 [PATCH v2] hw/net/virtio-net: add support for notification coalescing Koushik Dutta
2026-03-12 10:17 ` Eugenio Perez Martin
2026-03-23 8:38 ` Koushik Dutta
2026-03-23 9:46 ` Eugenio Perez Martin
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox