hv_netvsc: Implement batching of receive completions

The existing code uses busy retry when unable to send out receive
completions due to full ring buffer. It also gives up retrying after limit
is reached, and causes receive buffer slots not being recycled.
This patch implements batching of receive completions. It also prevents
dropping receive completions due to full ring buffer.
Signed-off-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Stephen Hemminger <sthemmin@microsoft.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/hyperv/hyperv_net.h

@@ -634,6 +634,20 @@ struct multi_send_data {
 	u32 count; /* counter of batched packets */
 };
 
+struct recv_comp_data {
+	u64 tid; /* transaction id */
+	u32 status;
+};
+
+/* Netvsc Receive Slots Max */
+#define NETVSC_RECVSLOT_MAX (NETVSC_RECEIVE_BUFFER_SIZE / ETH_DATA_LEN + 1)
+
+struct multi_recv_comp {
+	void *buf; /* queued receive completions */
+	u32 first; /* first data entry */
+	u32 next; /* next entry for writing */
+};
+
 struct netvsc_stats {
 	u64 packets;
 	u64 bytes;
@@ -736,6 +750,9 @@ struct netvsc_device {
 	u32 max_pkt; /* max number of pkt in one send, e.g. 8 */
 	u32 pkt_align; /* alignment bytes, e.g. 8 */
 
+	struct multi_recv_comp mrc[VRSS_CHANNEL_MAX];
+	atomic_t num_outstanding_recvs;
+
 	atomic_t open_cnt;
 };
 

drivers/net/hyperv/netvsc.c

@@ -74,6 +74,9 @@ static struct netvsc_device *alloc_net_device(void)
 		return NULL;
 	}
 
+	net_device->mrc[0].buf = vzalloc(NETVSC_RECVSLOT_MAX *
+					 sizeof(struct recv_comp_data));
+
 	init_waitqueue_head(&net_device->wait_drain);
 	net_device->destroy = false;
 	atomic_set(&net_device->open_cnt, 0);
@@ -85,6 +88,11 @@ static struct netvsc_device *alloc_net_device(void)
 
 static void free_netvsc_device(struct netvsc_device *nvdev)
 {
+	int i;
+
+	for (i = 0; i < VRSS_CHANNEL_MAX; i++)
+		vfree(nvdev->mrc[i].buf);
+
 	kfree(nvdev->cb_buffer);
 	kfree(nvdev);
 }
@@ -107,7 +115,8 @@ static struct netvsc_device *get_inbound_net_device(struct hv_device *device)
 		goto get_in_err;
 
 	if (net_device->destroy &&
-		atomic_read(&net_device->num_outstanding_sends) == 0)
+	    atomic_read(&net_device->num_outstanding_sends) == 0 &&
+	    atomic_read(&net_device->num_outstanding_recvs) == 0)
 		net_device = NULL;
 
 get_in_err:
@@ -972,49 +981,121 @@ int netvsc_send(struct hv_device *device,
 	return ret;
 }
 
-static void netvsc_send_recv_completion(struct hv_device *device,
-					struct vmbus_channel *channel,
-					struct netvsc_device *net_device,
+static int netvsc_send_recv_completion(struct vmbus_channel *channel,
 				       u64 transaction_id, u32 status)
 {
 	struct nvsp_message recvcompMessage;
-	int retries = 0;
 	int ret;
-	struct net_device *ndev = hv_get_drvdata(device);
 
 	recvcompMessage.hdr.msg_type =
 				NVSP_MSG1_TYPE_SEND_RNDIS_PKT_COMPLETE;
 
 	recvcompMessage.msg.v1_msg.send_rndis_pkt_complete.status = status;
 
-retry_send_cmplt:
 	/* Send the completion */
 	ret = vmbus_sendpacket(channel, &recvcompMessage,
-			       sizeof(struct nvsp_message), transaction_id,
-			       VM_PKT_COMP, 0);
-	if (ret == 0) {
-		/* success */
-		/* no-op */
-	} else if (ret == -EAGAIN) {
-		/* no more room...wait a bit and attempt to retry 3 times */
-		retries++;
-		netdev_err(ndev, "unable to send receive completion pkt"
-			" (tid %llx)...retrying %d\n", transaction_id, retries);
-
-		if (retries < 4) {
-			udelay(100);
-			goto retry_send_cmplt;
-		} else {
-			netdev_err(ndev, "unable to send receive "
-				"completion pkt (tid %llx)...give up retrying\n",
-				transaction_id);
-		}
-	} else {
-		netdev_err(ndev, "unable to send receive "
-			"completion pkt - %llx\n", transaction_id);
+			       sizeof(struct nvsp_message_header) + sizeof(u32),
+			       transaction_id, VM_PKT_COMP, 0);
+
+	return ret;
+}
+
+static inline void count_recv_comp_slot(struct netvsc_device *nvdev, u16 q_idx,
+					u32 *filled, u32 *avail)
+{
+	u32 first = nvdev->mrc[q_idx].first;
+	u32 next = nvdev->mrc[q_idx].next;
+
+	*filled = (first > next) ? NETVSC_RECVSLOT_MAX - first + next :
+		  next - first;
+
+	*avail = NETVSC_RECVSLOT_MAX - *filled - 1;
+}
+
+/* Read the first filled slot, no change to index */
+static inline struct recv_comp_data *read_recv_comp_slot(struct netvsc_device
+							 *nvdev, u16 q_idx)
+{
+	u32 filled, avail;
+
+	if (!nvdev->mrc[q_idx].buf)
+		return NULL;
+
+	count_recv_comp_slot(nvdev, q_idx, &filled, &avail);
+	if (!filled)
+		return NULL;
+
+	return nvdev->mrc[q_idx].buf + nvdev->mrc[q_idx].first *
+	       sizeof(struct recv_comp_data);
+}
+
+/* Put the first filled slot back to available pool */
+static inline void put_recv_comp_slot(struct netvsc_device *nvdev, u16 q_idx)
+{
+	int num_recv;
+
+	nvdev->mrc[q_idx].first = (nvdev->mrc[q_idx].first + 1) %
+				  NETVSC_RECVSLOT_MAX;
+
+	num_recv = atomic_dec_return(&nvdev->num_outstanding_recvs);
+
+	if (nvdev->destroy && num_recv == 0)
+		wake_up(&nvdev->wait_drain);
+}
+
+/* Check and send pending recv completions */
+static void netvsc_chk_recv_comp(struct netvsc_device *nvdev,
+				 struct vmbus_channel *channel, u16 q_idx)
+{
+	struct recv_comp_data *rcd;
+	int ret;
+
+	while (true) {
+		rcd = read_recv_comp_slot(nvdev, q_idx);
+		if (!rcd)
+			break;
+
+		ret = netvsc_send_recv_completion(channel, rcd->tid,
+						  rcd->status);
+		if (ret)
+			break;
+
+		put_recv_comp_slot(nvdev, q_idx);
 	}
 }
 
+#define NETVSC_RCD_WATERMARK 80
+
+/* Get next available slot */
+static inline struct recv_comp_data *get_recv_comp_slot(
+	struct netvsc_device *nvdev, struct vmbus_channel *channel, u16 q_idx)
+{
+	u32 filled, avail, next;
+	struct recv_comp_data *rcd;
+
+	if (!nvdev->recv_section)
+		return NULL;
+
+	if (!nvdev->mrc[q_idx].buf)
+		return NULL;
+
+	if (atomic_read(&nvdev->num_outstanding_recvs) >
+	    nvdev->recv_section->num_sub_allocs * NETVSC_RCD_WATERMARK / 100)
+		netvsc_chk_recv_comp(nvdev, channel, q_idx);
+
+	count_recv_comp_slot(nvdev, q_idx, &filled, &avail);
+	if (!avail)
+		return NULL;
+
+	next = nvdev->mrc[q_idx].next;
+	rcd = nvdev->mrc[q_idx].buf + next * sizeof(struct recv_comp_data);
+	nvdev->mrc[q_idx].next = (next + 1) % NETVSC_RECVSLOT_MAX;
+
+	atomic_inc(&nvdev->num_outstanding_recvs);
+
+	return rcd;
+}
+
 static void netvsc_receive(struct netvsc_device *net_device,
 			struct vmbus_channel *channel,
 			struct hv_device *device,
@@ -1029,6 +1110,9 @@ static void netvsc_receive(struct netvsc_device *net_device,
 	int count = 0;
 	struct net_device *ndev = hv_get_drvdata(device);
 	void *data;
+	int ret;
+	struct recv_comp_data *rcd;
+	u16 q_idx = channel->offermsg.offer.sub_channel_index;
 
 	/*
 	 * All inbound packets other than send completion should be xfer page
@@ -1076,8 +1160,26 @@ static void netvsc_receive(struct netvsc_device *net_device,
 
 	}
 
-	netvsc_send_recv_completion(device, channel, net_device,
-				    vmxferpage_packet->d.trans_id, status);
+	if (!net_device->mrc[q_idx].buf) {
+		ret = netvsc_send_recv_completion(channel,
+						  vmxferpage_packet->d.trans_id,
+						  status);
+		if (ret)
+			netdev_err(ndev, "Recv_comp q:%hd, tid:%llx, err:%d\n",
+				   q_idx, vmxferpage_packet->d.trans_id, ret);
+		return;
+	}
+
+	rcd = get_recv_comp_slot(net_device, channel, q_idx);
+
+	if (!rcd) {
+		netdev_err(ndev, "Recv_comp full buf q:%hd, tid:%llx\n",
+			   q_idx, vmxferpage_packet->d.trans_id);
+		return;
+	}
+
+	rcd->tid = vmxferpage_packet->d.trans_id;
+	rcd->status = status;
 }
 
 
@@ -1166,6 +1268,7 @@ void netvsc_channel_cb(void *context)
 {
 	int ret;
 	struct vmbus_channel *channel = (struct vmbus_channel *)context;
+	u16 q_idx = channel->offermsg.offer.sub_channel_index;
 	struct hv_device *device;
 	struct netvsc_device *net_device;
 	u32 bytes_recvd;
@@ -1245,6 +1348,9 @@ void netvsc_channel_cb(void *context)
 
 	if (bufferlen > NETVSC_PACKET_SIZE)
 		kfree(buffer);
+
+	netvsc_chk_recv_comp(net_device, channel, q_idx);
+
 	return;
 }
 

drivers/net/hyperv/rndis_filter.c

@@ -897,7 +897,8 @@ static void rndis_filter_halt_device(struct rndis_device *dev)
 
 	/* Wait for all send completions */
 	wait_event(nvdev->wait_drain,
-		atomic_read(&nvdev->num_outstanding_sends) == 0);
+		   atomic_read(&nvdev->num_outstanding_sends) == 0 &&
+		   atomic_read(&nvdev->num_outstanding_recvs) == 0);
 
 	if (request)
 		put_rndis_request(dev, request);
@@ -953,6 +954,9 @@ static void netvsc_sc_open(struct vmbus_channel *new_sc)
 	set_per_channel_state(new_sc, nvscdev->sub_cb_buf + (chn_index - 1) *
 			      NETVSC_PACKET_SIZE);
 
+	nvscdev->mrc[chn_index].buf = vzalloc(NETVSC_RECVSLOT_MAX *
+					      sizeof(struct recv_comp_data));
+
 	ret = vmbus_open(new_sc, nvscdev->ring_size * PAGE_SIZE,
 			 nvscdev->ring_size * PAGE_SIZE, NULL, 0,
 			 netvsc_channel_cb, new_sc);