net: reimplement softnet_data.output_queue as a FIFO queue

reimplement softnet_data.output_queue as a FIFO queue to keep the
fairness among the qdiscs rescheduled.

Signed-off-by: Changli Gao <[e-mail]>
Acked-by: Eric Dumazet <[e-mail]>
----
include/linux/netdevice.h | 1 +
net/core/dev.c | 22 ++++++++++++----------
2 files changed, 13 insertions(+), 10 deletions(-)
Signed-off-by: David S. Miller <[e-mail]>

include/linux/netdevice.h

···
  */
 struct softnet_data {
 	struct Qdisc		*output_queue;
+	struct Qdisc		**output_queue_tailp;
 	struct list_head	poll_list;
 	struct sk_buff		*completion_queue;
 

net/core/dev.c

···
 
 	local_irq_save(flags);
 	sd = &__get_cpu_var(softnet_data);
-	q->next_sched = sd->output_queue;
-	sd->output_queue = q;
+	q->next_sched = NULL;
+	*sd->output_queue_tailp = q;
+	sd->output_queue_tailp = &q->next_sched;
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_restore(flags);
 }
···
 		local_irq_disable();
 		head = sd->output_queue;
 		sd->output_queue = NULL;
+		sd->output_queue_tailp = &sd->output_queue;
 		local_irq_enable();
 
 		while (head) {
···
 			    void *ocpu)
 {
 	struct sk_buff **list_skb;
-	struct Qdisc **list_net;
 	struct sk_buff *skb;
 	unsigned int cpu, oldcpu = (unsigned long)ocpu;
 	struct softnet_data *sd, *oldsd;
···
 	*list_skb = oldsd->completion_queue;
 	oldsd->completion_queue = NULL;
 
-	/* Find end of our output_queue. */
-	list_net = &sd->output_queue;
-	while (*list_net)
-		list_net = &(*list_net)->next_sched;
 	/* Append output queue from offline CPU. */
-	*list_net = oldsd->output_queue;
-	oldsd->output_queue = NULL;
+	if (oldsd->output_queue) {
+		*sd->output_queue_tailp = oldsd->output_queue;
+		sd->output_queue_tailp = oldsd->output_queue_tailp;
+		oldsd->output_queue = NULL;
+		oldsd->output_queue_tailp = &oldsd->output_queue;
+	}
 
 	raise_softirq_irqoff(NET_TX_SOFTIRQ);
 	local_irq_enable();
···
 		skb_queue_head_init(&sd->input_pkt_queue);
 		sd->completion_queue = NULL;
 		INIT_LIST_HEAD(&sd->poll_list);
-
+		sd->output_queue = NULL;
+		sd->output_queue_tailp = &sd->output_queue;
 #ifdef CONFIG_RPS
 		sd->csd.func = rps_trigger_softirq;
 		sd->csd.info = sd;