Eliminate the throttling behaviour when the netif receive queue
fills because it behaves badly when using high speed networks under load.
The throttling cause multiple packet drops that cause TCP to go into
slow start mode. The same effective patch has been part of BIC TCP
and H-TCP as part of Web100.

Signed-off-by: Stephen Hemmminger <shemminger@osdl.org>


Index: linux-2.6.12-rc4-tcp2/net/core/dev.c
===================================================================
--- linux-2.6.12-rc4-tcp2.orig/net/core/dev.c
+++ linux-2.6.12-rc4-tcp2/net/core/dev.c
@@ -198,7 +198,7 @@ static struct notifier_block *netdev_cha
  *	Device drivers call our routines to queue packets here. We empty the
  *	queue in the local softnet handler.
  */
-DEFINE_PER_CPU(struct softnet_data, softnet_data) = { 0, };
+DEFINE_PER_CPU(struct softnet_data, softnet_data) = { NULL };
 
 #ifdef CONFIG_SYSFS
 extern int netdev_sysfs_init(void);
@@ -1360,7 +1360,6 @@ DEFINE_PER_CPU(struct netif_rx_stats, ne
 
 int netif_rx(struct sk_buff *skb)
 {
-	int this_cpu;
 	struct softnet_data *queue;
 	unsigned long flags;
 
@@ -1376,15 +1375,11 @@ int netif_rx(struct sk_buff *skb)
 	 * short when CPU is congested, but is still operating.
 	 */
 	local_irq_save(flags);
-	this_cpu = smp_processor_id();
 	queue = &__get_cpu_var(softnet_data);
 
 	__get_cpu_var(netdev_rx_stat).total++;
 	if (queue->input_pkt_queue.qlen <= netdev_max_backlog) {
 		if (queue->input_pkt_queue.qlen) {
-			if (queue->throttle)
-				goto drop;
-
 enqueue:
 			dev_hold(skb->dev);
 			__skb_queue_tail(&queue->input_pkt_queue, skb);
@@ -1392,19 +1387,10 @@ enqueue:
 			return NET_RX_SUCCESS;
 		}
 
-		if (queue->throttle)
-			queue->throttle = 0;
-
 		netif_rx_schedule(&queue->backlog_dev);
 		goto enqueue;
 	}
 
-	if (!queue->throttle) {
-		queue->throttle = 1;
-		__get_cpu_var(netdev_rx_stat).throttled++;
-	}
-
-drop:
 	__get_cpu_var(netdev_rx_stat).dropped++;
 	local_irq_restore(flags);
 
@@ -1688,8 +1674,6 @@ job_done:
 	smp_mb__before_clear_bit();
 	netif_poll_enable(backlog_dev);
 
-	if (queue->throttle)
-		queue->throttle = 0;
 	local_irq_enable();
 	return 0;
 }
@@ -1963,7 +1947,7 @@ static int softnet_seq_show(struct seq_f
 	struct netif_rx_stats *s = v;
 
 	seq_printf(seq, "%08x %08x %08x %08x %08x %08x %08x %08x %08x\n",
-		   s->total, s->dropped, s->time_squeeze, s->throttled,
+		   s->total, s->dropped, s->time_squeeze, 0,
 		   0, 0, 0, 0, /* was fastroute */
 		   s->cpu_collision );
 	return 0;
@@ -3207,7 +3191,6 @@ static int __init net_dev_init(void)
 
 		queue = &per_cpu(softnet_data, i);
 		skb_queue_head_init(&queue->input_pkt_queue);
-		queue->throttle = 0;
 		queue->completion_queue = NULL;
 		INIT_LIST_HEAD(&queue->poll_list);
 		set_bit(__LINK_STATE_START, &queue->backlog_dev.state);
Index: linux-2.6.12-rc4-tcp2/include/linux/netdevice.h
===================================================================
--- linux-2.6.12-rc4-tcp2.orig/include/linux/netdevice.h
+++ linux-2.6.12-rc4-tcp2/include/linux/netdevice.h
@@ -164,7 +164,6 @@ struct netif_rx_stats
 	unsigned total;
 	unsigned dropped;
 	unsigned time_squeeze;
-	unsigned throttled;
 	unsigned cpu_collision;
 };
 
@@ -557,10 +556,9 @@ static inline int unregister_gifconf(uns
 
 struct softnet_data
 {
-	int			throttle;
+	struct net_device	*output_queue;
 	struct sk_buff_head	input_pkt_queue;
 	struct list_head	poll_list;
-	struct net_device	*output_queue;
 	struct sk_buff		*completion_queue;
 
 	struct net_device	backlog_dev;	/* Sorry. 8) */