[PATCH] net: eliminate refcounting in backlog queue
From: Stephen Hemminger <hidden>
Date: 2008-07-25 19:32:14
Avoid the overhead of atomic increment/decrement on each received packet. This helps performance of non-NAPI devices (like loopback). Use cleanup function to walk queue on each cpu and clean out any left over packets. Signed-off-by: Stephen Hemminger <redacted>
--- a/net/core/dev.c 2008-07-25 11:27:07.000000000 -0700
+++ b/net/core/dev.c 2008-07-25 11:43:55.000000000 -0700@@ -1909,7 +1909,6 @@ int netif_rx(struct sk_buff *skb) if (queue->input_pkt_queue.qlen <= netdev_max_backlog) { if (queue->input_pkt_queue.qlen) { enqueue: - dev_hold(skb->dev); __skb_queue_tail(&queue->input_pkt_queue, skb); local_irq_restore(flags); return NET_RX_SUCCESS;
@@ -2270,6 +2269,20 @@ out: return ret; } +/* Network device is going away, flush any packets still pending */ +static void flush_backlog(void *arg) +{ + struct net_device *dev = arg; + struct softnet_data *queue = &__get_cpu_var(softnet_data); + struct sk_buff *skb, *tmp; + + skb_queue_walk_safe(&queue->input_pkt_queue, skb, tmp) + if (skb->dev == dev) { + __skb_unlink(skb, &queue->input_pkt_queue); + kfree_skb(skb); + } +} + static int process_backlog(struct napi_struct *napi, int quota) { int work = 0;
@@ -2279,7 +2292,6 @@ static int process_backlog(struct napi_s napi->weight = weight_p; do { struct sk_buff *skb; - struct net_device *dev; local_irq_disable(); skb = __skb_dequeue(&queue->input_pkt_queue);
@@ -2288,14 +2300,9 @@ static int process_backlog(struct napi_s local_irq_enable(); break; } - local_irq_enable(); - dev = skb->dev; - netif_receive_skb(skb); - - dev_put(dev); } while (++work < quota && jiffies == start_time); return work;
@@ -4165,6 +4172,8 @@ void netdev_run_todo(void) dev->reg_state = NETREG_UNREGISTERED; + on_each_cpu(flush_backlog, dev, 1); + netdev_wait_allrefs(dev); /* paranoia */