netdev - [PATCH net-next v2 1/2] virtio_net: enable irq for the control vq

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Date: Wed,  5 Jun 2024 22:55:32 +0800
From: Heng Qi <hengqi@...ux.alibaba.com>
To: netdev@...r.kernel.org,
	virtualization@...ts.linux.dev
Cc: Jason Wang <jasowang@...hat.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	Eric Dumazet <edumazet@...gle.com>,
	"David S. Miller" <davem@...emloft.net>,
	Jakub Kicinski <kuba@...nel.org>,
	Paolo Abeni <pabeni@...hat.com>
Subject: [PATCH net-next v2 1/2] virtio_net: enable irq for the control vq

If the device does not respond to a request for a long time,
then control vq polling elevates CPU utilization, a problem that
exacerbates with more command requests.

Enabling control vq's irq is advantageous for the guest, and
this still doesn't support concurrent requests.

This code is basically from Jason:
https://lore.kernel.org/all/20230413064027.13267-3-jasowang@redhat.com/

Suggested-by: Jason Wang <jasowang@...hat.com>
Signed-off-by: Heng Qi <hengqi@...ux.alibaba.com>
---
 drivers/net/virtio_net.c | 23 ++++++++++++++---------
 1 file changed, 14 insertions(+), 9 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4a802c0ea2cb..9b556ce89546 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -418,6 +418,9 @@ struct virtnet_info {
 	/* Lock to protect the control VQ */
 	struct mutex cvq_lock;
 
+	/* Wait for the device to complete the cvq request. */
+	struct completion completion;
+
 	/* Host can handle any s/g split between our header and packet data */
 	bool any_header_sg;
 
@@ -664,6 +667,13 @@ 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;
+
+	complete(&vi->completion);
+}
+
 static void skb_xmit_done(struct virtqueue *vq)
 {
 	struct virtnet_info *vi = vq->vdev->priv;
@@ -2721,14 +2731,8 @@ static bool virtnet_send_command_reply(struct virtnet_info *vi, u8 class, u8 cmd
 	if (unlikely(!virtqueue_kick(vi->cvq)))
 		goto unlock;
 
-	/* 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();
-	}
+	wait_for_completion(&vi->completion);
+	virtqueue_get_buf(vi->cvq, &tmp);
 
 unlock:
 	mutex_unlock(&vi->cvq_lock);
@@ -5312,7 +5316,7 @@ 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";
 	}
 
@@ -5832,6 +5836,7 @@ static int virtnet_probe(struct virtio_device *vdev)
 	if (vi->has_rss || vi->has_rss_hash_report)
 		virtnet_init_default_rss(vi);
 
+	init_completion(&vi->completion);
 	enable_rx_mode_work(vi);
 
 	/* serialize netdev register + virtio_device_ready() with ndo_open() */
-- 
2.32.0.3.g01195cf9f