net: use listified RX for handling GRO_NORMAL skbs

When GRO decides not to coalesce a packet, in napi_frags_finish(), instead
 of passing it to the stack immediately, place it on a list in the napi
 struct.  Then, at flush time (napi_complete_done(), napi_poll(), or
 napi_busy_loop()), call netif_receive_skb_list_internal() on the list.
We'd like to do that in napi_gro_flush(), but it's not called if
 !napi->gro_bitmask, so we have to do it in the callers instead.  (There are
 a handful of drivers that call napi_gro_flush() themselves, but it's not
 clear why, or whether this will affect them.)
Because a full 64 packets is an inefficiently large batch, also consume the
 list whenever it exceeds gro_normal_batch, a new net/core sysctl that
 defaults to 8.
Signed-off-by: NEdward Cree <ecree@solarflare.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -332,6 +332,8 @@ struct napi_struct {
 	struct net_device	*dev;
 	struct gro_list		gro_hash[GRO_HASH_BUCKETS];
 	struct sk_buff		*skb;
+	struct list_head	rx_list; /* Pending GRO_NORMAL skbs */
+	int			rx_count; /* length of rx_list */
 	struct hrtimer		timer;
 	struct list_head	dev_list;
 	struct hlist_node	napi_hash_node;
@@ -4239,6 +4241,7 @@ extern int		dev_weight_rx_bias;
 extern int		dev_weight_tx_bias;
 extern int		dev_rx_weight;
 extern int		dev_tx_weight;
+extern int		gro_normal_batch;
 
 bool netdev_has_upper_dev(struct net_device *dev, struct net_device *upper_dev);
 struct net_device *netdev_upper_get_next_dev_rcu(struct net_device *dev,

net/core/dev.c

@@ -3963,6 +3963,8 @@ int dev_weight_rx_bias __read_mostly = 1;  /* bias for backlog weight */
 int dev_weight_tx_bias __read_mostly = 1;  /* bias for output_queue quota */
 int dev_rx_weight __read_mostly = 64;
 int dev_tx_weight __read_mostly = 64;
+/* Maximum number of GRO_NORMAL skbs to batch up for list-RX */
+int gro_normal_batch __read_mostly = 8;
 
 /* Called with irq disabled */
 static inline void ____napi_schedule(struct softnet_data *sd,
@@ -5747,6 +5749,26 @@ struct sk_buff *napi_get_frags(struct napi_struct *napi)
 }
 EXPORT_SYMBOL(napi_get_frags);
 
+/* Pass the currently batched GRO_NORMAL SKBs up to the stack. */
+static void gro_normal_list(struct napi_struct *napi)
+{
+	if (!napi->rx_count)
+		return;
+	netif_receive_skb_list_internal(&napi->rx_list);
+	INIT_LIST_HEAD(&napi->rx_list);
+	napi->rx_count = 0;
+}
+
+/* Queue one GRO_NORMAL SKB up for list processing.  If batch size exceeded,
+ * pass the whole batch up to the stack.
+ */
+static void gro_normal_one(struct napi_struct *napi, struct sk_buff *skb)
+{
+	list_add_tail(&skb->list, &napi->rx_list);
+	if (++napi->rx_count >= gro_normal_batch)
+		gro_normal_list(napi);
+}
+
 static gro_result_t napi_frags_finish(struct napi_struct *napi,
 				      struct sk_buff *skb,
 				      gro_result_t ret)
@@ -5756,8 +5778,8 @@ static gro_result_t napi_frags_finish(struct napi_struct *napi,
 	case GRO_HELD:
 		__skb_push(skb, ETH_HLEN);
 		skb->protocol = eth_type_trans(skb, skb->dev);
-		if (ret == GRO_NORMAL && netif_receive_skb_internal(skb))
-			ret = GRO_DROP;
+		if (ret == GRO_NORMAL)
+			gro_normal_one(napi, skb);
 		break;
 
 	case GRO_DROP:
@@ -6034,6 +6056,8 @@ bool napi_complete_done(struct napi_struct *n, int work_done)
 				 NAPIF_STATE_IN_BUSY_POLL)))
 		return false;
 
+	gro_normal_list(n);
+
 	if (n->gro_bitmask) {
 		unsigned long timeout = 0;
 
@@ -6119,10 +6143,19 @@ static void busy_poll_stop(struct napi_struct *napi, void *have_poll_lock)
 	 * Ideally, a new ndo_busy_poll_stop() could avoid another round.
 	 */
 	rc = napi->poll(napi, BUSY_POLL_BUDGET);
+	/* We can't gro_normal_list() here, because napi->poll() might have
+	 * rearmed the napi (napi_complete_done()) in which case it could
+	 * already be running on another CPU.
+	 */
 	trace_napi_poll(napi, rc, BUSY_POLL_BUDGET);
 	netpoll_poll_unlock(have_poll_lock);
-	if (rc == BUSY_POLL_BUDGET)
+	if (rc == BUSY_POLL_BUDGET) {
+		/* As the whole budget was spent, we still own the napi so can
+		 * safely handle the rx_list.
+		 */
+		gro_normal_list(napi);
 		__napi_schedule(napi);
+	}
 	local_bh_enable();
 }
 
@@ -6167,6 +6200,7 @@ void napi_busy_loop(unsigned int napi_id,
 		}
 		work = napi_poll(napi, BUSY_POLL_BUDGET);
 		trace_napi_poll(napi, work, BUSY_POLL_BUDGET);
+		gro_normal_list(napi);
 count:
 		if (work > 0)
 			__NET_ADD_STATS(dev_net(napi->dev),
@@ -6272,6 +6306,8 @@ void netif_napi_add(struct net_device *dev, struct napi_struct *napi,
 	napi->timer.function = napi_watchdog;
 	init_gro_hash(napi);
 	napi->skb = NULL;
+	INIT_LIST_HEAD(&napi->rx_list);
+	napi->rx_count = 0;
 	napi->poll = poll;
 	if (weight > NAPI_POLL_WEIGHT)
 		netdev_err_once(dev, "%s() called with weight %d\n", __func__,
@@ -6368,6 +6404,8 @@ static int napi_poll(struct napi_struct *n, struct list_head *repoll)
 		goto out_unlock;
 	}
 
+	gro_normal_list(n);
+
 	if (n->gro_bitmask) {
 		/* flush too old packets
 		 * If HZ < 1000, flush all packets.

net/core/sysctl_net_core.c

@@ -567,6 +567,14 @@ static struct ctl_table net_core_table[] = {
 		.mode		= 0644,
 		.proc_handler	= proc_do_static_key,
 	},
+	{
+		.procname	= "gro_normal_batch",
+		.data		= &gro_normal_batch,
+		.maxlen		= sizeof(unsigned int),
+		.mode		= 0644,
+		.proc_handler	= proc_dointvec_minmax,
+		.extra1		= SYSCTL_ONE,
+	},
 	{ }
 };