[PATCH 1/3] Remove the TX timer from virtio_net

[Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>]

Doing tx mitigation in the host gets equivalent performance and offers greater
flexibility.  It also simplifies the guest code.

Signed-off-by: Anthony Liguori <aliguori-r/Jw6+rmf7HQT0dZR+AlfA@public.gmane.org>

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 4082099..797a3ed 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -23,7 +23,6 @@
 #include <linux/virtio.h>
 #include <linux/virtio_net.h>
 #include <linux/scatterlist.h>
-#include <linux/hrtimer.h>
 
 static int napi_weight = 128;
 module_param(napi_weight, int, 0444);
@@ -40,15 +39,9 @@ struct virtnet_info
 	struct net_device *dev;
 	struct napi_struct napi;
 
-	/* TX coalescing. */
-	struct hrtimer tx_timer;
-
 	/* Number of input buffers, and max we've ever had. */
 	unsigned int num, max;
 
-	/* Number of queued output buffers, and max we've ever had. */
-	unsigned int out_num, out_max;
-
 	/* Receive & send queues. */
 	struct sk_buff_head recv;
 	struct sk_buff_head send;
@@ -238,20 +231,6 @@ again:
 	return received;
 }
 
-static enum hrtimer_restart kick_xmit(struct hrtimer *t)
-{
-	struct virtnet_info *vi = container_of(t,struct virtnet_info,tx_timer);
-
-	BUG_ON(!in_softirq());
-	BUG_ON(in_irq());
-	netif_tx_lock(vi->dev);
-	vi->svq->vq_ops->kick(vi->svq);
-	vi->out_num = 0;
-	netif_tx_unlock(vi->dev);
-
-	return HRTIMER_NORESTART;
-}
-
 static int start_xmit(struct sk_buff *skb, struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
@@ -305,13 +284,8 @@ again:
 			goto again;
 
 		pr_debug("%s: virtio not prepared to send\n", dev->name);
-		if (vi->out_max != vi->out_num)
-			printk("%s: out_max changed from %u to %u\n",
-			       dev->name, vi->out_max, vi->out_num);
-		vi->out_max = vi->out_num;
-		vi->out_num = 0;
+
 		/* Kick off send immediately. */
-		hrtimer_cancel(&vi->tx_timer);
 		vi->svq->vq_ops->kick(vi->svq);
 		netif_stop_queue(dev);
 
@@ -327,13 +301,8 @@ again:
 		return NETDEV_TX_BUSY;
 	}
 
-	if (++vi->out_num == vi->out_max) {
-		hrtimer_cancel(&vi->tx_timer);
-		vi->svq->vq_ops->kick(vi->svq);
-		vi->out_num = 0;
-	} else if (!hrtimer_is_queued(&vi->tx_timer))
-		hrtimer_start(&vi->tx_timer, ktime_set(0,500000),
-			      HRTIMER_MODE_REL);
+	vi->svq->vq_ops->kick(vi->svq);
+
 	return 0;
 }
 
@@ -425,10 +394,6 @@ static int virtnet_probe(struct virtio_device *vdev)
 	netif_napi_add(dev, &vi->napi, virtnet_poll, napi_weight);
 	vi->dev = dev;
 	vi->vdev = vdev;
-	memset(&vi->tx_timer, 0, sizeof(vi->tx_timer));
-	hrtimer_init(&vi->tx_timer, CLOCK_REALTIME, HRTIMER_MODE_REL);
-	vi->tx_timer.function = kick_xmit;
-	vi->out_max = -1U;
 
 	/* We expect two virtqueues, receive then send. */
 	vi->rvq = vdev->config->find_vq(vdev, 0, skb_recv_done);

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