[PATCH net-next 1/3] virtio_net: enable irq for the control vq

[Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>]

Control vq polling request results consume more CPU.
Especially when dim issues more control requests to the device,
it's beneficial to the guest to enable control vq's irq.

Suggested-by: Jason Wang <jasowang@xxxxxxxxxx>
Signed-off-by: Heng Qi <hengqi@xxxxxxxxxxxxxxxxx>
---
 drivers/net/virtio_net.c | 45 ++++++++++++++++++++++++++++++----------
 1 file changed, 34 insertions(+), 11 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index a4d3c76654a4..79a1b30c173c 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -287,6 +287,12 @@ struct virtnet_info {
 	bool has_cvq;
 	struct mutex cvq_lock;
 
+	/* Wait for the device to complete the request */
+	struct completion completion;
+
+	/* Work struct for acquisition of cvq processing results. */
+	struct work_struct get_cvq;
+
 	/* Host can handle any s/g split between our header and packet data */
 	bool any_header_sg;
 
@@ -520,6 +526,13 @@ static bool virtqueue_napi_complete(struct napi_struct *napi,
 	return false;
 }
 
+static void virtnet_cvq_done(struct virtqueue *cvq)
+{
+	struct virtnet_info *vi = cvq->vdev->priv;
+
+	schedule_work(&vi->get_cvq);
+}
+
 static void skb_xmit_done(struct virtqueue *vq)
 {
 	struct virtnet_info *vi = vq->vdev->priv;
@@ -2036,6 +2049,20 @@ static bool try_fill_recv(struct virtnet_info *vi, struct receive_queue *rq,
 	return !oom;
 }
 
+static void virtnet_get_cvq_work(struct work_struct *work)
+{
+	struct virtnet_info *vi =
+		container_of(work, struct virtnet_info, get_cvq);
+	unsigned int tmp;
+	void *res;
+
+	mutex_lock(&vi->cvq_lock);
+	res = virtqueue_get_buf(vi->cvq, &tmp);
+	if (res)
+		complete(&vi->completion);
+	mutex_unlock(&vi->cvq_lock);
+}
+
 static void skb_recv_done(struct virtqueue *rvq)
 {
 	struct virtnet_info *vi = rvq->vdev->priv;
@@ -2531,7 +2558,7 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
 				 struct scatterlist *out)
 {
 	struct scatterlist *sgs[4], hdr, stat;
-	unsigned out_num = 0, tmp;
+	unsigned out_num = 0;
 	int ret;
 
 	/* Caller should know better */
@@ -2566,16 +2593,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd,
 		return vi->ctrl->status == VIRTIO_NET_OK;
 	}
 
-	/* Spin for a response, the kick causes an ioport write, trapping
-	 * into the hypervisor, so the request should be handled immediately.
-	 */
-	while (!virtqueue_get_buf(vi->cvq, &tmp) &&
-	       !virtqueue_is_broken(vi->cvq)) {
-		cond_resched();
-		cpu_relax();
-	}
-
 	mutex_unlock(&vi->cvq_lock);
+
+	wait_for_completion(&vi->completion);
+
 	return vi->ctrl->status == VIRTIO_NET_OK;
 }
 
@@ -4433,7 +4454,7 @@ static int virtnet_find_vqs(struct virtnet_info *vi)
 
 	/* Parameters for control virtqueue, if any */
 	if (vi->has_cvq) {
-		callbacks[total_vqs - 1] = NULL;
+		callbacks[total_vqs - 1] = virtnet_cvq_done;
 		names[total_vqs - 1] = "control";
 	}
 
@@ -4952,6 +4973,8 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (vi->has_rss || vi->has_rss_hash_report)
 		virtnet_init_default_rss(vi);
 
+	INIT_WORK(&vi->get_cvq, virtnet_get_cvq_work);
+	init_completion(&vi->completion);
 	enable_rx_mode_work(vi);
 
 	/* serialize netdev register + virtio_device_ready() with ndo_open() */
-- 
2.32.0.3.g01195cf9f