[PATCH net-next] virtio-net: rx busy polling support

[Jason Wang]

Add basic support for rx busy polling.

1 byte netperf tcp_rr on mlx4 shows 116% improvement: the transaction
rate was increased from 9151.94 to 19787.37.

Cc: Rusty Russell <rusty@xxxxxxxxxxxxxxx>
Cc: Michael S. Tsirkin <mst@xxxxxxxxxx>
Cc: Vlad Yasevich <vyasevic@xxxxxxxxxx>
Signed-off-by: Jason Wang <jasowang@xxxxxxxxxx>
---
 drivers/net/virtio_net.c | 241 +++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 225 insertions(+), 16 deletions(-)

diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c
index 7d9f84a..a5ce604 100644
--- a/drivers/net/virtio_net.c
+++ b/drivers/net/virtio_net.c
@@ -27,6 +27,7 @@
 #include <linux/slab.h>
 #include <linux/cpu.h>
 #include <linux/average.h>
+#include <net/busy_poll.h>
 
 static int napi_weight = NAPI_POLL_WEIGHT;
 module_param(napi_weight, int, 0444);
@@ -94,8 +95,144 @@ struct receive_queue {
 
 	/* Name of this receive queue: input.$index */
 	char name[40];
+
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	unsigned int state;
+#define VIRTNET_RQ_STATE_IDLE        0
+#define VIRTNET_RQ_STATE_NAPI	     1    /* NAPI or refill owns this RQ */
+#define VIRTNET_RQ_STATE_POLL	     2    /* poll owns this RQ */
+#define VIRTNET_RQ_STATE_DISABLED    4    /* RQ is disabled */
+#define VIRTNET_RQ_OWNED (VIRTNET_RQ_STATE_NAPI | VIRTNET_RQ_STATE_POLL)
+#define VIRTNET_RQ_LOCKED (VIRTNET_RQ_OWNED | VIRTNET_RQ_STATE_DISABLED)
+#define VIRTNET_RQ_STATE_NAPI_YIELD  8    /* NAPI or refill yielded this RQ */
+#define VIRTNET_RQ_STATE_POLL_YIELD  16   /* poll yielded this RQ */
+#define VIRTNET_RQ_YIELD (VIRTNET_RQ_STATE_NAPI_YIELD | VIRTNET_RQ_STATE_POLL_YIELD)
+	spinlock_t lock;
+#endif  /* CONFIG_NET_RX_BUSY_POLL */
 };
 
+#ifdef CONFIG_NET_RX_BUSY_POLL
+static inline void virtnet_rq_init_lock(struct receive_queue *rq)
+{
+
+	spin_lock_init(&rq->lock);
+	rq->state = VIRTNET_RQ_STATE_IDLE;
+}
+
+/* called from the device poll routine or refill routine to get ownership of a
+ * receive queue.
+ */
+static inline bool virtnet_rq_lock_napi_refill(struct receive_queue *rq)
+{
+	int rc = true;
+
+	spin_lock(&rq->lock);
+	if (rq->state & VIRTNET_RQ_LOCKED) {
+		WARN_ON(rq->state & VIRTNET_RQ_STATE_NAPI);
+		rq->state |= VIRTNET_RQ_STATE_NAPI_YIELD;
+		rc = false;
+	} else
+		/* we don't care if someone yielded */
+		rq->state = VIRTNET_RQ_STATE_NAPI;
+	spin_unlock(&rq->lock);
+	return rc;
+}
+
+/* returns true is someone tried to get the rq while napi or refill had it */
+static inline bool virtnet_rq_unlock_napi_refill(struct receive_queue *rq)
+{
+	int rc = false;
+
+	spin_lock(&rq->lock);
+	WARN_ON(rq->state & (VIRTNET_RQ_STATE_POLL |
+			     VIRTNET_RQ_STATE_NAPI_YIELD));
+
+	if (rq->state & VIRTNET_RQ_STATE_POLL_YIELD)
+		rc = true;
+	/* will reset state to idle, unless RQ is disabled */
+	rq->state &= VIRTNET_RQ_STATE_DISABLED;
+	spin_unlock(&rq->lock);
+	return rc;
+}
+
+/* called from virtnet_low_latency_recv() */
+static inline bool virtnet_rq_lock_poll(struct receive_queue *rq)
+{
+	int rc = true;
+
+	spin_lock_bh(&rq->lock);
+	if ((rq->state & VIRTNET_RQ_LOCKED)) {
+		rq->state |= VIRTNET_RQ_STATE_POLL_YIELD;
+		rc = false;
+	} else
+		/* preserve yield marks */
+		rq->state |= VIRTNET_RQ_STATE_POLL;
+	spin_unlock_bh(&rq->lock);
+	return rc;
+}
+
+/* returns true if someone tried to get the receive queue while it was locked */
+static inline bool virtnet_rq_unlock_poll(struct receive_queue *rq)
+{
+	int rc = false;
+
+	spin_lock_bh(&rq->lock);
+	WARN_ON(rq->state & (VIRTNET_RQ_STATE_NAPI));
+
+	if (rq->state & VIRTNET_RQ_STATE_POLL_YIELD)
+		rc = true;
+	/* will reset state to idle, unless RQ is disabled */
+	rq->state &= VIRTNET_RQ_STATE_DISABLED;
+	spin_unlock_bh(&rq->lock);
+	return rc;
+}
+
+/* return false if RQ is currently owned */
+static inline bool virtnet_rq_disable(struct receive_queue *rq)
+{
+	int rc = true;
+
+	spin_lock_bh(&rq->lock);
+	if (rq->state & VIRTNET_RQ_OWNED)
+		rc = false;
+	rq->state |= VIRTNET_RQ_STATE_DISABLED;
+	spin_unlock_bh(&rq->lock);
+
+	return rc;
+}
+
+#else /* CONFIG_NET_RX_BUSY_POLL */
+static inline void virtnet_rq_init_lock(struct receive_queue *rq)
+{
+}
+
+static inline bool virtnet_rq_lock_napi_refill(struct receive_queue *rq)
+{
+	return true;
+}
+
+static inline bool virtnet_rq_unlock_napi_refill(struct receive_queue *rq)
+{
+	return false;
+}
+
+static inline bool virtnet_rq_lock_poll(struct receive_queue *rq)
+{
+	return false;
+}
+
+static inline bool virtnet_rq_unlock_poll(struct receive_queue *rq)
+{
+	return false;
+}
+
+static inline bool virtnet_rq_disable(struct receive_queue *rq)
+{
+	return true;
+}
+
+#endif /* CONFIG_NET_RX_BUSY_POLL */
+
 struct virtnet_info {
 	struct virtio_device *vdev;
 	struct virtqueue *cvq;
@@ -521,6 +658,8 @@ static void receive_buf(struct receive_queue *rq, void *buf, unsigned int len)
 		skb_shinfo(skb)->gso_segs = 0;
 	}
 
+	skb_mark_napi_id(skb, &rq->napi);
+
 	netif_receive_skb(skb);
 	return;
 
@@ -714,7 +853,12 @@ static void refill_work(struct work_struct *work)
 		struct receive_queue *rq = &vi->rq[i];
 
 		napi_disable(&rq->napi);
+		if (!virtnet_rq_lock_napi_refill(rq)) {
+			virtnet_napi_enable(rq);
+			continue;
+		}
 		still_empty = !try_fill_recv(rq, GFP_KERNEL);
+		virtnet_rq_unlock_napi_refill(rq);
 		virtnet_napi_enable(rq);
 
 		/* In theory, this can happen: if we don't get any buffers in
@@ -725,16 +869,13 @@ static void refill_work(struct work_struct *work)
 	}
 }
 
-static int virtnet_poll(struct napi_struct *napi, int budget)
+static int virtnet_receive(struct receive_queue *rq, int budget)
 {
-	struct receive_queue *rq =
-		container_of(napi, struct receive_queue, napi);
 	struct virtnet_info *vi = rq->vq->vdev->priv;
 	void *buf;
-	unsigned int r, len, received = 0;
+	unsigned int len, received = 0;
 
-again:
-	while (received < budget &&
+	while ((received < budget) &&
 	       (buf = virtqueue_get_buf(rq->vq, &len)) != NULL) {
 		receive_buf(rq, buf, len);
 		received++;
@@ -745,6 +886,24 @@ again:
 			schedule_delayed_work(&vi->refill, 0);
 	}
 
+	return received;
+}
+
+static int virtnet_poll(struct napi_struct *napi, int budget)
+{
+	struct receive_queue *rq =
+		container_of(napi, struct receive_queue, napi);
+	unsigned int r, received = 0;
+
+again:
+
+	if (!virtnet_rq_lock_napi_refill(rq))
+		return budget;
+
+	received = virtnet_receive(rq, budget);
+
+	virtnet_rq_unlock_napi_refill(rq);
+
 	/* Out of packets? */
 	if (received < budget) {
 		r = virtqueue_enable_cb_prepare(rq->vq);
@@ -760,6 +919,52 @@ again:
 	return received;
 }
 
+#ifdef CONFIG_NET_RX_BUSY_POLL
+/* must be called with local_bh_disable()d */
+static int virtnet_low_latency_recv(struct napi_struct *napi)
+{
+	struct receive_queue *rq =
+		container_of(napi, struct receive_queue, napi);
+	struct virtnet_info *vi = rq->vq->vdev->priv;
+	int received;
+
+	if (!(vi->status & VIRTIO_NET_S_LINK_UP))
+		return LL_FLUSH_FAILED;
+
+	if (!virtnet_rq_lock_poll(rq))
+		return LL_FLUSH_BUSY;
+
+	received = virtnet_receive(rq, 4);
+
+	virtnet_rq_unlock_poll(rq);
+
+	return received;
+}
+#endif	/* CONFIG_NET_RX_BUSY_POLL */
+
+static void virtnet_napi_enable_all(struct virtnet_info *vi)
+{
+	int i;
+
+	for (i = 0; i < vi->max_queue_pairs; i++) {
+		virtnet_rq_init_lock(&vi->rq[i]);
+		virtnet_napi_enable(&vi->rq[i]);
+	}
+}
+
+static void virtnet_napi_disable_all(struct virtnet_info *vi)
+{
+	int i;
+
+	for (i = 0; i < vi->max_queue_pairs; i++) {
+		napi_disable(&vi->rq[i].napi);
+		while (!virtnet_rq_disable(&vi->rq[i])) {
+			pr_info("RQ %d locked\n", i);
+			usleep_range(1000, 20000);
+		}
+	}
+}
+
 static int virtnet_open(struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
@@ -770,9 +975,10 @@ static int virtnet_open(struct net_device *dev)
 			/* Make sure we have some buffers: if oom use wq. */
 			if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
 				schedule_delayed_work(&vi->refill, 0);
-		virtnet_napi_enable(&vi->rq[i]);
 	}
 
+	virtnet_napi_enable_all(vi);
+
 	return 0;
 }
 
@@ -1076,13 +1282,11 @@ static int virtnet_set_queues(struct virtnet_info *vi, u16 queue_pairs)
 static int virtnet_close(struct net_device *dev)
 {
 	struct virtnet_info *vi = netdev_priv(dev);
-	int i;
 
 	/* Make sure refill_work doesn't re-enable napi! */
 	cancel_delayed_work_sync(&vi->refill);
 
-	for (i = 0; i < vi->max_queue_pairs; i++)
-		napi_disable(&vi->rq[i].napi);
+	virtnet_napi_disable_all(vi);
 
 	return 0;
 }
@@ -1347,6 +1551,9 @@ static const struct net_device_ops virtnet_netdev = {
 #ifdef CONFIG_NET_POLL_CONTROLLER
 	.ndo_poll_controller = virtnet_netpoll,
 #endif
+#ifdef CONFIG_NET_RX_BUSY_POLL
+	.ndo_busy_poll		= virtnet_low_latency_recv,
+#endif
 };
 
 static void virtnet_config_changed_work(struct work_struct *work)
@@ -1552,6 +1759,7 @@ static int virtnet_alloc_queues(struct virtnet_info *vi)
 		vi->rq[i].pages = NULL;
 		netif_napi_add(vi->dev, &vi->rq[i].napi, virtnet_poll,
 			       napi_weight);
+		napi_hash_add(&vi->rq[i].napi);
 
 		sg_init_table(vi->rq[i].sg, ARRAY_SIZE(vi->rq[i].sg));
 		ewma_init(&vi->rq[i].mrg_avg_pkt_len, 1, RECEIVE_AVG_WEIGHT);
@@ -1854,10 +2062,12 @@ static int virtnet_freeze(struct virtio_device *vdev)
 	cancel_delayed_work_sync(&vi->refill);
 
 	if (netif_running(vi->dev))
-		for (i = 0; i < vi->max_queue_pairs; i++) {
-			napi_disable(&vi->rq[i].napi);
-			netif_napi_del(&vi->rq[i].napi);
-		}
+		virtnet_napi_disable_all(vi);
+
+	for (i = 0; i < vi->max_queue_pairs; i++) {
+		napi_hash_del(&vi->rq[i].napi);
+		netif_napi_del(&vi->rq[i].napi);
+	}
 
 	remove_vq_common(vi);
 
@@ -1880,8 +2090,7 @@ static int virtnet_restore(struct virtio_device *vdev)
 			if (!try_fill_recv(&vi->rq[i], GFP_KERNEL))
 				schedule_delayed_work(&vi->refill, 0);
 
-		for (i = 0; i < vi->max_queue_pairs; i++)
-			virtnet_napi_enable(&vi->rq[i]);
+		virtnet_napi_enable_all(vi);
 	}
 
 	netif_device_attach(vi->dev);
-- 
1.9.1

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