The feature supports two coalescing modes: - Time-based: delay notifications up to N microseconds - Count-based: delay until N packets are processed
Implementation details: - Added VIRTIO_NET_CTRL_NOTF_COAL class handling in control virtqueue - RX path: batches notifications based on packet count or timeout - TX path: leverages the unified dispatcher to dynamically enable timer-based coalescing when guest configures it via ethtool - Coalescing parameters persist across live migration Note: When tx=timer is configured at VM launch, the coalescing feature is automatically disabled because tx=timer already introduces a fixed 150µs delay for packet batching, making notification coalescing redundant. Adds the `x-vq_notf_coal=on` device parameter to dynamically enable virtqueue notification coalescing at VM startup. Performance metrics (Moderate Coalescing vs Without Coalescing): - RX parameters: 1000µs, 10 frames - TX parameters: 2000µs, 20 frames - Results: 20% drop in CPU overhead and a 30% reduction in interrupts. Signed-off-by: Koushik Dutta <[email protected]> --- hw/net/virtio-net.c | 203 ++++++++++++++++++++++++++++++++- include/hw/virtio/virtio-net.h | 10 ++ net/passt.c | 1 + net/tap.c | 1 + net/vhost-user.c | 1 + net/vhost-vdpa.c | 1 + 6 files changed, 213 insertions(+), 4 deletions(-) diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c index e7f05956a5..fac1013d47 100644 --- a/hw/net/virtio-net.c +++ b/hw/net/virtio-net.c @@ -157,6 +157,16 @@ 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) +{ + VirtIONetQueue *q = opaque; + VirtIONet *n = q->n; + VirtIODevice *vdev = VIRTIO_DEVICE(n); + + q->rx_coal.pkt_cnt = 0; + virtio_notify(vdev, q->rx_vq); +} + static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config) { VirtIONet *n = VIRTIO_NET(vdev); @@ -1002,6 +1012,87 @@ static void virtio_net_set_features(VirtIODevice *vdev, } } +static void virtio_net_tx_notification_timer(void *opaque) +{ + VirtIONetQueue *q = opaque; + VirtIONet *n = q->n; + VirtIODevice *vdev = VIRTIO_DEVICE(n); + + q->tx_coal.pkt_cnt = 0; + virtio_notify(vdev, q->tx_vq); +} + +static bool virtio_net_tx_should_notify(VirtIONetQueue *q) +{ + if (q->tx_coal.usecs == 0 || !q->tx_coal.timer) { + return true; + } + + q->tx_coal.pkt_cnt++; + + if (q->tx_coal.packets > 0 && q->tx_coal.pkt_cnt >= q->tx_coal.packets) { + q->tx_coal.pkt_cnt = 0; + timer_del(q->tx_coal.timer); + return true; + } + + if (!timer_pending(q->tx_coal.timer)) { + timer_mod(q->tx_coal.timer, + qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + + q->tx_coal.usecs * 1000); /* Converted to ns */ + } + + return false; +} + +static int virtio_net_handle_coal(VirtIONet *n, uint8_t cmd, + struct iovec *iov, unsigned int iov_cnt) +{ + struct virtio_net_ctrl_coal coal; + VirtIONetQueue *q; + size_t s; + int i; + + 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) { + for (i = 0; i < n->max_queue_pairs; i++) { + q = &n->vqs[i]; + q->rx_coal.usecs = le32_to_cpu(coal.max_usecs); + q->rx_coal.packets = le32_to_cpu(coal.max_packets); + q->rx_coal.pkt_cnt = 0; + if (q->rx_coal.usecs > 0) { + /* Delete old timer if exists, then create new one */ + g_clear_pointer(&q->rx_coal.timer, timer_free); + q->rx_coal.timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, + virtio_net_rx_notify, + q); + } else { + g_clear_pointer(&q->rx_coal.timer, timer_free); + } + } + } else if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_TX_SET) { + for (i = 0; i < n->max_queue_pairs; i++) { + q = &n->vqs[i]; + q->tx_coal.usecs = le32_to_cpu(coal.max_usecs); + q->tx_coal.packets = le32_to_cpu(coal.max_packets); + q->tx_coal.pkt_cnt = 0; + if (q->tx_coal.usecs > 0) { + g_clear_pointer(&q->tx_coal.timer, timer_free); + q->tx_coal.timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, + virtio_net_tx_notification_timer, + q); + } else { + g_clear_pointer(&q->tx_coal.timer, timer_free); + } + } + } + return VIRTIO_NET_OK; +} + static int virtio_net_handle_rx_mode(VirtIONet *n, uint8_t cmd, struct iovec *iov, unsigned int iov_cnt) { @@ -1581,6 +1672,8 @@ 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)); @@ -2040,7 +2133,23 @@ 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 */ + q->rx_coal.pkt_cnt += i; + if (q->rx_coal.usecs == 0 || q->rx_coal.pkt_cnt >= q->rx_coal.packets) { + if (q->rx_coal.timer) { + timer_del(q->rx_coal.timer); + } + virtio_net_rx_notify(q); + } else { + if (q->rx_coal.timer) { + if (!timer_pending(q->rx_coal.timer)) { + timer_mod(q->rx_coal.timer, + qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + + q->rx_coal.usecs * 1000); /* Converted to ns */ + } + } + } return size; @@ -2690,7 +2799,9 @@ static void virtio_net_tx_complete(NetClientState *nc, ssize_t len) int ret; virtqueue_push(q->tx_vq, q->async_tx.elem, 0); - virtio_notify(vdev, q->tx_vq); + if (virtio_net_tx_should_notify(q)) { + virtio_notify(vdev, q->tx_vq); + } g_free(q->async_tx.elem); q->async_tx.elem = NULL; @@ -2802,7 +2913,10 @@ static int32_t virtio_net_flush_tx(VirtIONetQueue *q) drop: virtqueue_push(q->tx_vq, elem, 0); - virtio_notify(vdev, q->tx_vq); + if (virtio_net_tx_should_notify(q)) { + virtio_notify(vdev, q->tx_vq); + } + g_free(elem); if (++num_packets >= n->tx_burst) { @@ -2899,6 +3013,7 @@ static void virtio_net_tx_timer(void *opaque) if (ret == -EBUSY || ret == -EINVAL) { return; } + /* * If we flush a full burst of packets, assume there are * more coming and immediately rearm @@ -3005,6 +3120,12 @@ static void virtio_net_add_queue(VirtIONet *n, int index) &DEVICE(vdev)->mem_reentrancy_guard); n->vqs[index].tx_waiting = 0; + n->vqs[index].rx_coal.pkt_cnt = 0; + n->vqs[index].tx_coal.pkt_cnt = 0; + n->vqs[index].rx_coal.usecs = 0; + n->vqs[index].tx_coal.usecs = 0; + n->vqs[index].rx_coal.packets = 0; + n->vqs[index].tx_coal.packets = 0; n->vqs[index].n = n; } @@ -3017,6 +3138,11 @@ static void virtio_net_del_queue(VirtIONet *n, int index) qemu_purge_queued_packets(nc); virtio_del_queue(vdev, index * 2); + + /* Cleanup coalescing timers */ + g_clear_pointer(&q->rx_coal.timer, timer_free); + g_clear_pointer(&q->tx_coal.timer, timer_free); + if (q->tx_timer) { timer_free(q->tx_timer); q->tx_timer = NULL; @@ -3097,6 +3223,13 @@ 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); + if (n->tx_timer_activate) { + virtio_clear_feature_ex(features, VIRTIO_NET_F_NOTF_COAL); + } else { + if (!virtio_has_feature(*features, VIRTIO_NET_F_NOTF_COAL)) { + *features &= ~(1ULL << VIRTIO_NET_F_NOTF_COAL); + } + } if (!peer_has_vnet_hdr(n)) { virtio_clear_feature_ex(features, VIRTIO_NET_F_CSUM); @@ -3251,6 +3384,26 @@ static int virtio_net_post_load_device(void *opaque, int version_id) } virtio_net_commit_rss_config(n); + + for (i = 0; i < n->max_queue_pairs; i++) { + VirtIONetQueue *q = &n->vqs[i]; + if (q->rx_coal.usecs > 0) { + if (!q->rx_coal.timer) { + q->rx_coal.timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, + virtio_net_rx_notify, + q); + } + } + + if (q->tx_coal.usecs > 0) { + if (!q->tx_coal.timer) { + q->tx_coal.timer = timer_new_ns(QEMU_CLOCK_VIRTUAL, + virtio_net_tx_notification_timer, + q); + } + } + } + return 0; } @@ -3270,13 +3423,49 @@ static int virtio_net_post_load_virtio(VirtIODevice *vdev) return 0; } +static const VMStateDescription vmstate_virtio_net_coal = { + .name = "virtio-net-coal", + .version_id = 1, + .minimum_version_id = 1, + .fields = (const VMStateField[]) { + VMSTATE_UINT32(usecs, VirtIONetCoal), + VMSTATE_UINT32(packets, VirtIONetCoal), + VMSTATE_UINT32(pkt_cnt, VirtIONetCoal), + VMSTATE_END_OF_LIST() + }, +}; + +static bool virtio_net_queue_notf_coal_needed(void *opaque) +{ + VirtIONetQueue *q = opaque; + return q->rx_coal.usecs > 0 || q->tx_coal.usecs > 0; +} + +static const VMStateDescription vmstate_virtio_net_queue_notf_coal = { + .name = "virtio-net-queue-tx_waiting/notf-coal", + .version_id = 1, + .minimum_version_id = 1, + .needed = virtio_net_queue_notf_coal_needed, + .fields = (const VMStateField[]) { + VMSTATE_STRUCT(rx_coal, VirtIONetQueue, 0, + vmstate_virtio_net_coal, VirtIONetCoal), + VMSTATE_STRUCT(tx_coal, VirtIONetQueue, 0, + vmstate_virtio_net_coal, VirtIONetCoal), + VMSTATE_END_OF_LIST() + }, +}; + /* tx_waiting field of a VirtIONetQueue */ static const VMStateDescription vmstate_virtio_net_queue_tx_waiting = { .name = "virtio-net-queue-tx_waiting", .fields = (const VMStateField[]) { VMSTATE_UINT32(tx_waiting, VirtIONetQueue), VMSTATE_END_OF_LIST() - }, + }, + .subsections = (const VMStateDescription * const []) { + &vmstate_virtio_net_queue_notf_coal, + NULL + } }; static bool max_queue_pairs_gt_1(void *opaque, int version_id) @@ -3981,6 +4170,10 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp) if (n->net_conf.tx && strcmp(n->net_conf.tx, "timer") == 0) { n->tx_timer_activate = true; + if (n->host_features & (1ULL << VIRTIO_NET_F_NOTF_COAL)) { + warn_report("virtio-net: 'vq_notf_coal' is incompatible with 'tx=timer'," + "disabling notification coalescing"); + } } n->net_conf.tx_queue_size = MIN(virtio_net_max_tx_queue_size(n), @@ -4271,6 +4464,8 @@ 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("x-vq_notf_coal", VirtIONet, host_features, + VIRTIO_NET_F_NOTF_COAL, false), DEFINE_PROP_ON_OFF_AUTO_BIT64("hash-ipv4", VirtIONet, rss_data.specified_hash_types, VIRTIO_NET_HASH_REPORT_IPv4 - 1, diff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h index a4eb3f407e..244c8a0224 100644 --- a/include/hw/virtio/virtio-net.h +++ b/include/hw/virtio/virtio-net.h @@ -155,6 +155,14 @@ typedef struct VirtioNetRssData { uint16_t default_queue; } VirtioNetRssData; +/* Interrupt notification coalescing parameters */ +typedef struct VirtIONetCoal { + uint32_t usecs; /* Timeout in microseconds */ + uint32_t packets; /* Packet count threshold */ + uint32_t pkt_cnt; /* Current packet count since last notification */ + QEMUTimer *timer; /* Coalescing timer */ +} VirtIONetCoal; + typedef struct VirtIONetQueue { VirtQueue *rx_vq; VirtQueue *tx_vq; @@ -165,6 +173,8 @@ typedef struct VirtIONetQueue { VirtQueueElement *elem; } async_tx; struct VirtIONet *n; + VirtIONetCoal rx_coal; + VirtIONetCoal tx_coal; } VirtIONetQueue; struct VirtIONet { diff --git a/net/passt.c b/net/passt.c index 45440c399b..43b36ed8c5 100644 --- a/net/passt.c +++ b/net/passt.c @@ -52,6 +52,7 @@ static const int user_feature_bits[] = { VIRTIO_NET_F_GUEST_USO4, VIRTIO_NET_F_GUEST_USO6, VIRTIO_NET_F_HOST_USO, + VIRTIO_NET_F_NOTF_COAL, /* This bit implies RARP isn't sent by QEMU out of band */ VIRTIO_NET_F_GUEST_ANNOUNCE, diff --git a/net/tap.c b/net/tap.c index 57ffb09885..e6ddbc1eb1 100644 --- a/net/tap.c +++ b/net/tap.c @@ -63,6 +63,7 @@ static const int kernel_feature_bits[] = { VIRTIO_F_NOTIFICATION_DATA, VIRTIO_NET_F_RSC_EXT, VIRTIO_NET_F_HASH_REPORT, + VIRTIO_NET_F_NOTF_COAL, VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO, VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO, VHOST_INVALID_FEATURE_BIT diff --git a/net/vhost-user.c b/net/vhost-user.c index 2d0fc49b4d..f1e9b7a038 100644 --- a/net/vhost-user.c +++ b/net/vhost-user.c @@ -54,6 +54,7 @@ static const int user_feature_bits[] = { VIRTIO_NET_F_GUEST_USO4, VIRTIO_NET_F_GUEST_USO6, VIRTIO_NET_F_HOST_USO, + VIRTIO_NET_F_NOTF_COAL, /* This bit implies RARP isn't sent by QEMU out of band */ VIRTIO_NET_F_GUEST_ANNOUNCE, diff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c index f1523697e2..0dcd6fb9f1 100644 --- a/net/vhost-vdpa.c +++ b/net/vhost-vdpa.c @@ -70,6 +70,7 @@ 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_NOTF_COAL, VIRTIO_NET_F_CTRL_VQ, VIRTIO_NET_F_GSO, VIRTIO_NET_F_GUEST_CSUM, -- 2.53.0
