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GET /api/1.2/patches/2222675/?format=api
HTTP 200 OK
Allow: GET, PUT, PATCH, HEAD, OPTIONS
Content-Type: application/json
Vary: Accept

{
    "id": 2222675,
    "url": "http://patchwork.ozlabs.org/api/1.2/patches/2222675/?format=api",
    "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260413121348.655887-1-kdutta@redhat.com/",
    "project": {
        "id": 14,
        "url": "http://patchwork.ozlabs.org/api/1.2/projects/14/?format=api",
        "name": "QEMU Development",
        "link_name": "qemu-devel",
        "list_id": "qemu-devel.nongnu.org",
        "list_email": "qemu-devel@nongnu.org",
        "web_url": "",
        "scm_url": "",
        "webscm_url": "",
        "list_archive_url": "",
        "list_archive_url_format": "",
        "commit_url_format": ""
    },
    "msgid": "<20260413121348.655887-1-kdutta@redhat.com>",
    "list_archive_url": null,
    "date": "2026-04-13T12:13:48",
    "name": "[v5] hw/net/virtio-net: add support for notification coalescing",
    "commit_ref": null,
    "pull_url": null,
    "state": "new",
    "archived": false,
    "hash": "9ccc95ef524e8a8236446600849623937da37143",
    "submitter": {
        "id": 92694,
        "url": "http://patchwork.ozlabs.org/api/1.2/people/92694/?format=api",
        "name": "Koushik Dutta",
        "email": "kdutta@redhat.com"
    },
    "delegate": null,
    "mbox": "http://patchwork.ozlabs.org/project/qemu-devel/patch/20260413121348.655887-1-kdutta@redhat.com/mbox/",
    "series": [
        {
            "id": 499690,
            "url": "http://patchwork.ozlabs.org/api/1.2/series/499690/?format=api",
            "web_url": "http://patchwork.ozlabs.org/project/qemu-devel/list/?series=499690",
            "date": "2026-04-13T12:13:48",
            "name": "[v5] hw/net/virtio-net: add support for notification coalescing",
            "version": 5,
            "mbox": "http://patchwork.ozlabs.org/series/499690/mbox/"
        }
    ],
    "comments": "http://patchwork.ozlabs.org/api/patches/2222675/comments/",
    "check": "pending",
    "checks": "http://patchwork.ozlabs.org/api/patches/2222675/checks/",
    "tags": {},
    "related": [],
    "headers": {
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        ],
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        "X-Mimecast-MFC-AGG-ID": "h7EgaVz5MeSsp_sUJYn_6Q_1776082435",
        "From": "Koushik Dutta <kdutta@redhat.com>",
        "To": "qemu-devel@nongnu.org",
        "Cc": "\"Michael S. Tsirkin\" <mst@redhat.com>, Jason Wang <jasowang@redhat.com>,\n Stefano Garzarella <sgarzare@redhat.com>,\n =?utf-8?q?Eugenio_P=C3=A9rez?= <eperezma@redhat.com>",
        "Subject": "[PATCH v5] hw/net/virtio-net: add support for notification coalescing",
        "Date": "Mon, 13 Apr 2026 17:43:48 +0530",
        "Message-ID": "<20260413121348.655887-1-kdutta@redhat.com>",
        "MIME-Version": "1.0",
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    },
    "content": "Implement VirtIO Network Notification Coalescing (Bit 53).\nThis allows the guest to manage interrupt frequency using ethtool\n-C for both RX and TX paths.\n\n- Added VIRTIO_NET_F_NOTF_COAL to host features.\n- Implemented VIRTIO_NET_CTRL_NOTF_COAL class handling in\n  virtio_net_handle_ctrl_iov.\n- Added logic to store and apply rx/tx usecs and max_packets.\n- Added packet counters and threshold logic for both RX and TX data paths.\n- Dynamic Dispatcher: Implemented a dispatcher mechanism that\n  dynamically switches/activates the notification callback logic\n  only after the guest enables TX coalescing via ethtool.\n- After VM LM coalescing parameters persist in the destination VM.\n\nThis reduces interrupt overhead by batching notifications based on\neither a packet count or a time-based threshold.\n\nSigned-off-by: Koushik Dutta <kdutta@redhat.com>\n---\n hw/net/virtio-net.c            | 180 ++++++++++++++++++++++++++++++---\n include/hw/virtio/virtio-net.h |   9 ++\n net/passt.c                    |   1 +\n net/tap.c                      |   1 +\n net/vhost-user.c               |   1 +\n net/vhost-vdpa.c               |   2 +\n 6 files changed, 178 insertions(+), 16 deletions(-)",
    "diff": "diff --git a/hw/net/virtio-net.c b/hw/net/virtio-net.c\nindex 2a5d642a64..a15e9d17bd 100644\n--- a/hw/net/virtio-net.c\n+++ b/hw/net/virtio-net.c\n@@ -157,6 +157,16 @@ static void flush_or_purge_queued_packets(NetClientState *nc)\n  * - we could suppress RX interrupt if we were so inclined.\n  */\n \n+static void virtio_net_rx_notify(void *opaque)\n+{\n+    VirtIONetQueue *q = opaque;\n+    VirtIONet *n = q->n;\n+    VirtIODevice *vdev = VIRTIO_DEVICE(n);\n+\n+    n->rx_pkt_cnt = 0;\n+    virtio_notify(vdev, q->rx_vq);\n+}\n+\n static void virtio_net_get_config(VirtIODevice *vdev, uint8_t *config)\n {\n     VirtIONet *n = VIRTIO_NET(vdev);\n@@ -1080,6 +1090,53 @@ static int virtio_net_handle_offloads(VirtIONet *n, uint8_t cmd,\n     }\n }\n \n+static void virtio_net_tx_timer(void *opaque);\n+\n+static int virtio_net_handle_coal(VirtIONet *n, uint8_t cmd,\n+                                  struct iovec *iov, unsigned int iov_cnt)\n+{\n+    struct virtio_net_ctrl_coal coal;\n+    VirtIONetQueue *q;\n+    size_t s;\n+    int i;\n+\n+    s = iov_to_buf(iov, iov_cnt, 0, &coal, sizeof(coal));\n+    if (s != sizeof(coal)) {\n+        return VIRTIO_NET_ERR;\n+    }\n+\n+    if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_RX_SET) {\n+        n->rx_coal_usecs = le32_to_cpu(coal.max_usecs);\n+        n->rx_coal_packets = le32_to_cpu(coal.max_packets);\n+        if (n->rx_coal_usecs > 0) {\n+            for (i = 0; i < n->max_queue_pairs; i++) {\n+                q = &n->vqs[i];\n+                if (!q->rx_timer) {\n+                    q->rx_timer = timer_new_us(QEMU_CLOCK_VIRTUAL,\n+                                               virtio_net_rx_notify,\n+                                               q);\n+                }\n+            }\n+        }\n+    } else if (cmd == VIRTIO_NET_CTRL_NOTF_COAL_TX_SET) {\n+        n->tx_coal_usecs = le32_to_cpu(coal.max_usecs);\n+        n->tx_coal_packets = le32_to_cpu(coal.max_packets);\n+        n->tx_timeout = n->tx_coal_usecs * 1000;\n+        if (n->tx_coal_usecs > 0) {\n+            for (i = 0; i < n->max_queue_pairs; i++) {\n+                q = &n->vqs[i];\n+                if (!q->tx_timer && n->tx_coal_usecs > 0) {\n+                    q->tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,\n+                                               virtio_net_tx_timer,\n+                                               q);\n+                }\n+            }\n+        }\n+    }\n+\n+    return VIRTIO_NET_OK;\n+}\n+\n static int virtio_net_handle_mac(VirtIONet *n, uint8_t cmd,\n                                  struct iovec *iov, unsigned int iov_cnt)\n {\n@@ -1581,6 +1638,8 @@ size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,\n         status = virtio_net_handle_mq(n, ctrl.cmd, iov, out_num);\n     } else if (ctrl.class == VIRTIO_NET_CTRL_GUEST_OFFLOADS) {\n         status = virtio_net_handle_offloads(n, ctrl.cmd, iov, out_num);\n+    } else if (ctrl.class == VIRTIO_NET_CTRL_NOTF_COAL) {\n+        status = virtio_net_handle_coal(n, ctrl.cmd, iov, out_num);\n     }\n \n     s = iov_from_buf(in_sg, in_num, 0, &status, sizeof(status));\n@@ -2040,7 +2099,22 @@ static ssize_t virtio_net_receive_rcu(NetClientState *nc, const uint8_t *buf,\n     }\n \n     virtqueue_flush(q->rx_vq, i);\n-    virtio_notify(vdev, q->rx_vq);\n+\n+    /* rx coalescing */\n+    n->rx_pkt_cnt += i;\n+    if (n->rx_coal_usecs == 0 || n->rx_pkt_cnt >= n->rx_coal_packets) {\n+        if (q->rx_timer) {\n+            timer_del(q->rx_timer);\n+        }\n+        virtio_net_rx_notify(q);\n+    } else {\n+        if (q->rx_timer) {\n+            if (!timer_pending(q->rx_timer)) {\n+                timer_mod(q->rx_timer,\n+                          qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) + n->rx_coal_usecs);\n+            }\n+        }\n+    }\n \n     return size;\n \n@@ -2817,7 +2891,6 @@ detach:\n     return -EINVAL;\n }\n \n-static void virtio_net_tx_timer(void *opaque);\n \n static void virtio_net_handle_tx_timer(VirtIODevice *vdev, VirtQueue *vq)\n {\n@@ -2899,6 +2972,12 @@ static void virtio_net_tx_timer(void *opaque)\n     if (ret == -EBUSY || ret == -EINVAL) {\n         return;\n     }\n+    if (n->tx_pkt_cnt < ret) {\n+        n->tx_pkt_cnt = 0;\n+    } else {\n+        n->tx_pkt_cnt -= ret;\n+    }\n+\n     /*\n      * If we flush a full burst of packets, assume there are\n      * more coming and immediately rearm\n@@ -2918,6 +2997,7 @@ static void virtio_net_tx_timer(void *opaque)\n     ret = virtio_net_flush_tx(q);\n     if (ret > 0) {\n         virtio_queue_set_notification(q->tx_vq, 0);\n+        n->tx_pkt_cnt -= ret;\n         q->tx_waiting = 1;\n         timer_mod(q->tx_timer,\n                   qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);\n@@ -2973,6 +3053,32 @@ static void virtio_net_tx_bh(void *opaque)\n     }\n }\n \n+static void virtio_net_handle_tx_dispatch(VirtIODevice *vdev, VirtQueue *vq)\n+{\n+    VirtIONet *n = VIRTIO_NET(vdev);\n+    VirtIONetQueue *q = &n->vqs[vq2q(virtio_get_queue_index(vq))];\n+    bool use_timer = n->tx_timer_activate || n->tx_coal_usecs > 0 ||\n+                     n->tx_coal_packets > 0;\n+    bool pkt_limit = (n->tx_coal_packets > 0);\n+\n+    if (use_timer) {\n+        n->tx_pkt_cnt++;\n+        if (!pkt_limit || n->tx_pkt_cnt < n->tx_coal_packets) {\n+            if (q->tx_timer) {\n+                virtio_net_handle_tx_timer(vdev, vq);\n+                return;\n+            }\n+        }\n+        n->tx_pkt_cnt = 0;\n+        if (q->tx_timer) {\n+            timer_del(q->tx_timer);\n+        }\n+        virtio_net_handle_tx_bh(vdev, vq);\n+    } else {\n+        virtio_net_handle_tx_bh(vdev, vq);\n+    }\n+}\n+\n static void virtio_net_add_queue(VirtIONet *n, int index)\n {\n     VirtIODevice *vdev = VIRTIO_DEVICE(n);\n@@ -2980,20 +3086,15 @@ static void virtio_net_add_queue(VirtIONet *n, int index)\n     n->vqs[index].rx_vq = virtio_add_queue(vdev, n->net_conf.rx_queue_size,\n                                            virtio_net_handle_rx);\n \n-    if (n->net_conf.tx && !strcmp(n->net_conf.tx, \"timer\")) {\n-        n->vqs[index].tx_vq =\n-            virtio_add_queue(vdev, n->net_conf.tx_queue_size,\n-                             virtio_net_handle_tx_timer);\n-        n->vqs[index].tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,\n-                                              virtio_net_tx_timer,\n-                                              &n->vqs[index]);\n-    } else {\n-        n->vqs[index].tx_vq =\n-            virtio_add_queue(vdev, n->net_conf.tx_queue_size,\n-                             virtio_net_handle_tx_bh);\n-        n->vqs[index].tx_bh = qemu_bh_new_guarded(virtio_net_tx_bh, &n->vqs[index],\n-                                                  &DEVICE(vdev)->mem_reentrancy_guard);\n-    }\n+    n->vqs[index].tx_vq =\n+        virtio_add_queue(vdev,\n+                         n->net_conf.tx_queue_size,\n+                         virtio_net_handle_tx_dispatch);\n+\n+    n->vqs[index].tx_bh =\n+        qemu_bh_new_guarded(virtio_net_tx_bh,\n+                            &n->vqs[index],\n+                            &DEVICE(vdev)->mem_reentrancy_guard);\n \n     n->vqs[index].tx_waiting = 0;\n     n->vqs[index].n = n;\n@@ -3242,6 +3343,36 @@ static int virtio_net_post_load_device(void *opaque, int version_id)\n     }\n \n     virtio_net_commit_rss_config(n);\n+    if (n->tx_coal_usecs > 0 || n->rx_coal_usecs > 0) {\n+        n->tx_timeout = n->tx_coal_usecs * 1000;\n+\n+        for (i = 0; i < n->max_queue_pairs; i++) {\n+            VirtIONetQueue *q = &n->vqs[i];\n+            if (!q->rx_timer && n->rx_coal_usecs > 0) {\n+                q->rx_timer = timer_new_us(QEMU_CLOCK_VIRTUAL,\n+                                           virtio_net_rx_notify,\n+                                           q);\n+            }\n+\n+            if (!q->tx_timer && n->tx_coal_usecs > 0) {\n+                q->tx_timer = timer_new_ns(QEMU_CLOCK_VIRTUAL,\n+                                           virtio_net_tx_timer,\n+                                           q);\n+            }\n+\n+            if (n->tx_coal_usecs > 0 && q->tx_timer) {\n+                n->tx_pkt_cnt = 0;\n+                timer_mod(q->tx_timer,\n+                          qemu_clock_get_ns(QEMU_CLOCK_VIRTUAL) + n->tx_timeout);\n+            }\n+\n+            if (n->rx_coal_usecs > 0 && q->rx_timer) {\n+                timer_mod(q->rx_timer,\n+                          qemu_clock_get_us(QEMU_CLOCK_VIRTUAL) + n->rx_coal_usecs);\n+            }\n+        }\n+    }\n+\n     return 0;\n }\n \n@@ -3617,6 +3748,10 @@ static const VMStateDescription vmstate_virtio_net_device = {\n                          vmstate_virtio_net_tx_waiting),\n         VMSTATE_UINT64_TEST(curr_guest_offloads, VirtIONet,\n                             has_ctrl_guest_offloads),\n+        VMSTATE_UINT32(rx_coal_usecs, VirtIONet),\n+        VMSTATE_UINT32(tx_coal_usecs, VirtIONet),\n+        VMSTATE_UINT32(rx_coal_packets, VirtIONet),\n+        VMSTATE_UINT32(tx_coal_packets, VirtIONet),\n         VMSTATE_END_OF_LIST()\n     },\n     .subsections = (const VMStateDescription * const []) {\n@@ -3970,6 +4105,10 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)\n         error_printf(\"Defaulting to \\\"bh\\\"\");\n     }\n \n+    if (n->net_conf.tx && strcmp(n->net_conf.tx, \"timer\")) {\n+        n->tx_timer_activate = true;\n+    }\n+\n     n->net_conf.tx_queue_size = MIN(virtio_net_max_tx_queue_size(n),\n                                     n->net_conf.tx_queue_size);\n \n@@ -4046,6 +4185,13 @@ static void virtio_net_device_realize(DeviceState *dev, Error **errp)\n             n->rss_data.specified_hash_types.on_bits |\n             n->rss_data.specified_hash_types.auto_bits;\n     }\n+    n->rx_pkt_cnt = 0;\n+    n->tx_pkt_cnt = 0;\n+    n->rx_coal_usecs = 0;\n+    n->tx_coal_usecs = 0;\n+    n->rx_coal_packets = 0;\n+    n->tx_coal_packets = 0;\n+    n->rx_index_timer = NULL;\n }\n \n static void virtio_net_device_unrealize(DeviceState *dev)\n@@ -4258,6 +4404,8 @@ static const Property virtio_net_properties[] = {\n                       VIRTIO_NET_F_GUEST_USO6, true),\n     DEFINE_PROP_BIT64(\"host_uso\", VirtIONet, host_features,\n                       VIRTIO_NET_F_HOST_USO, true),\n+    DEFINE_PROP_BIT64(\"vq_notf_coal\", VirtIONet, host_features,\n+                      VIRTIO_NET_F_NOTF_COAL, true),\n     DEFINE_PROP_ON_OFF_AUTO_BIT64(\"hash-ipv4\", VirtIONet,\n                                   rss_data.specified_hash_types,\n                                   VIRTIO_NET_HASH_REPORT_IPv4 - 1,\ndiff --git a/include/hw/virtio/virtio-net.h b/include/hw/virtio/virtio-net.h\nindex 371e376428..d88f8aef87 100644\n--- a/include/hw/virtio/virtio-net.h\n+++ b/include/hw/virtio/virtio-net.h\n@@ -158,6 +158,7 @@ typedef struct VirtioNetRssData {\n typedef struct VirtIONetQueue {\n     VirtQueue *rx_vq;\n     VirtQueue *tx_vq;\n+    QEMUTimer *rx_timer;\n     QEMUTimer *tx_timer;\n     QEMUBH *tx_bh;\n     uint32_t tx_waiting;\n@@ -230,6 +231,14 @@ struct VirtIONet {\n     struct EBPFRSSContext ebpf_rss;\n     uint32_t nr_ebpf_rss_fds;\n     char **ebpf_rss_fds;\n+    QEMUTimer *rx_index_timer;\n+    uint32_t rx_coal_usecs;\n+    uint32_t rx_coal_packets;\n+    uint32_t rx_pkt_cnt;\n+    uint32_t tx_coal_usecs;\n+    uint32_t tx_coal_packets;\n+    uint32_t tx_pkt_cnt;\n+    bool tx_timer_activate;\n };\n \n size_t virtio_net_handle_ctrl_iov(VirtIODevice *vdev,\ndiff --git a/net/passt.c b/net/passt.c\nindex 4ff94ee509..0b0d9e222a 100644\n--- a/net/passt.c\n+++ b/net/passt.c\n@@ -52,6 +52,7 @@ static const int user_feature_bits[] = {\n     VIRTIO_NET_F_GUEST_USO4,\n     VIRTIO_NET_F_GUEST_USO6,\n     VIRTIO_NET_F_HOST_USO,\n+    VIRTIO_NET_F_NOTF_COAL,\n \n     /* This bit implies RARP isn't sent by QEMU out of band */\n     VIRTIO_NET_F_GUEST_ANNOUNCE,\ndiff --git a/net/tap.c b/net/tap.c\nindex 8d7ab6ba6f..ea5987a3dc 100644\n--- a/net/tap.c\n+++ b/net/tap.c\n@@ -62,6 +62,7 @@ static const int kernel_feature_bits[] = {\n     VIRTIO_F_NOTIFICATION_DATA,\n     VIRTIO_NET_F_RSC_EXT,\n     VIRTIO_NET_F_HASH_REPORT,\n+    VIRTIO_NET_F_NOTF_COAL,\n     VIRTIO_NET_F_GUEST_UDP_TUNNEL_GSO,\n     VIRTIO_NET_F_HOST_UDP_TUNNEL_GSO,\n     VHOST_INVALID_FEATURE_BIT\ndiff --git a/net/vhost-user.c b/net/vhost-user.c\nindex a4bb49bbcf..f0b3752d7c 100644\n--- a/net/vhost-user.c\n+++ b/net/vhost-user.c\n@@ -54,6 +54,7 @@ static const int user_feature_bits[] = {\n     VIRTIO_NET_F_GUEST_USO4,\n     VIRTIO_NET_F_GUEST_USO6,\n     VIRTIO_NET_F_HOST_USO,\n+    VIRTIO_NET_F_NOTF_COAL,\n \n     /* This bit implies RARP isn't sent by QEMU out of band */\n     VIRTIO_NET_F_GUEST_ANNOUNCE,\ndiff --git a/net/vhost-vdpa.c b/net/vhost-vdpa.c\nindex 3df6091274..a20db78b81 100644\n--- a/net/vhost-vdpa.c\n+++ b/net/vhost-vdpa.c\n@@ -70,6 +70,7 @@ static const int vdpa_feature_bits[] = {\n     VIRTIO_NET_F_CTRL_RX,\n     VIRTIO_NET_F_CTRL_RX_EXTRA,\n     VIRTIO_NET_F_CTRL_VLAN,\n+    VIRTIO_NET_F_NOTF_COAL,\n     VIRTIO_NET_F_CTRL_VQ,\n     VIRTIO_NET_F_GSO,\n     VIRTIO_NET_F_GUEST_CSUM,\n@@ -115,6 +116,7 @@ static const uint64_t vdpa_svq_device_features =\n     BIT_ULL(VIRTIO_NET_F_HOST_UFO) |\n     BIT_ULL(VIRTIO_NET_F_MRG_RXBUF) |\n     BIT_ULL(VIRTIO_NET_F_STATUS) |\n+    BIT_ULL(VIRTIO_NET_F_NOTF_COAL) |\n     BIT_ULL(VIRTIO_NET_F_CTRL_VQ) |\n     BIT_ULL(VIRTIO_NET_F_GSO) |\n     BIT_ULL(VIRTIO_NET_F_CTRL_RX) |\n",
    "prefixes": [
        "v5"
    ]
}