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Date: Wed, 5 Nov 2008 12:36:59 -0800
From: Stephen Hemminger <shemminger@...tta.com>
To: Stephen Hemminger <shemminger@...tta.com>
Cc: David Miller <davem@...emloft.net>, netdev@...r.kernel.org
Subject: [RFC] loopback: optimization
Convert loopback device from using common network queues to a per-cpu
receive queue with NAPI. This gives a small 1% performance gain when
measured over 5 runs of tbench. Not sure if it's worth bothering
though.
Signed-off-by: Stephen Hemminger <shemminger@...tta.com>
--- a/drivers/net/loopback.c 2008-11-04 15:36:29.000000000 -0800
+++ b/drivers/net/loopback.c 2008-11-05 10:00:20.000000000 -0800
@@ -59,7 +59,10 @@
#include <linux/percpu.h>
#include <net/net_namespace.h>
-struct pcpu_lstats {
+struct loopback_queue {
+ struct sk_buff_head rxq;
+ struct napi_struct napi;
+
unsigned long packets;
unsigned long bytes;
};
@@ -70,36 +73,60 @@ struct pcpu_lstats {
*/
static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
{
- struct pcpu_lstats *pcpu_lstats, *lb_stats;
+ struct loopback_queue *pcpu;
skb_orphan(skb);
skb->protocol = eth_type_trans(skb,dev);
- /* it's OK to use per_cpu_ptr() because BHs are off */
- pcpu_lstats = dev->ml_priv;
- lb_stats = per_cpu_ptr(pcpu_lstats, smp_processor_id());
- lb_stats->bytes += skb->len;
- lb_stats->packets++;
-
- netif_rx(skb);
+ pcpu = per_cpu_ptr(dev->ml_priv, smp_processor_id());
+ if (likely(pcpu->rxq.qlen <= netdev_max_backlog)) {
+ __skb_queue_tail(&pcpu->rxq, skb);
+ pcpu->bytes += skb->len;
+ pcpu->packets++;
+ napi_schedule_irq(&pcpu->napi);
+
+ return NET_XMIT_SUCCESS;
+ } else {
+ dev->stats.rx_dropped++;
+ dev_kfree_skb_any(skb);
+ return NET_XMIT_DROP;
+ }
return 0;
}
+static int loopback_poll(struct napi_struct *arg, int quota)
+{
+ struct loopback_queue *pcpu = container_of(arg, struct loopback_queue, napi);
+ int work = 0;
+
+ do {
+ struct sk_buff *skb = __skb_dequeue(&pcpu->rxq);
+
+ if (!skb) {
+ __napi_complete(arg);
+ break;
+ }
+
+ netif_receive_skb(skb);
+ } while (++work < quota);
+
+ return work;
+}
+
+
static struct net_device_stats *get_stats(struct net_device *dev)
{
- const struct pcpu_lstats *pcpu_lstats;
struct net_device_stats *stats = &dev->stats;
unsigned long bytes = 0;
unsigned long packets = 0;
int i;
- pcpu_lstats = dev->ml_priv;
for_each_possible_cpu(i) {
- const struct pcpu_lstats *lb_stats;
+ const struct loopback_queue *lb_stats;
- lb_stats = per_cpu_ptr(pcpu_lstats, i);
+ lb_stats = per_cpu_ptr(dev->ml_priv, i);
bytes += lb_stats->bytes;
packets += lb_stats->packets;
}
@@ -125,21 +152,57 @@ static const struct ethtool_ops loopback
static int loopback_dev_init(struct net_device *dev)
{
- struct pcpu_lstats *lstats;
+ void *p;
+ int i;
- lstats = alloc_percpu(struct pcpu_lstats);
- if (!lstats)
+ p = alloc_percpu(struct loopback_queue);
+ if (!p)
return -ENOMEM;
- dev->ml_priv = lstats;
+ for_each_possible_cpu(i) {
+ struct loopback_queue *pcpu = per_cpu_ptr(p, i);
+ skb_queue_head_init(&pcpu->rxq);
+ netif_napi_add(dev, &pcpu->napi, loopback_poll, 64);
+ }
+
+ dev->ml_priv = p;
+
+ return 0;
+}
+
+static int loopback_dev_start(struct net_device *dev)
+{
+ int i;
+
+ for_each_possible_cpu(i) {
+ struct loopback_queue *pcpu = per_cpu_ptr(dev->ml_priv, i);
+ napi_enable(&pcpu->napi);
+ }
+ return 0;
+}
+
+static int loopback_dev_stop(struct net_device *dev)
+{
+ int i;
+
+ for_each_possible_cpu(i) {
+ struct loopback_queue *pcpu = per_cpu_ptr(dev->ml_priv, i);
+ napi_disable(&pcpu->napi);
+ __skb_queue_purge(&pcpu->rxq);
+ }
return 0;
}
static void loopback_dev_free(struct net_device *dev)
{
- struct pcpu_lstats *lstats = dev->ml_priv;
+ int i;
+
+ for_each_possible_cpu(i) {
+ struct loopback_queue *pcpu = per_cpu_ptr(dev->ml_priv, i);
+ napi_disable(&pcpu->napi);
+ }
- free_percpu(lstats);
+ free_percpu(dev->ml_priv);
free_netdev(dev);
}
@@ -166,6 +229,8 @@ static void loopback_setup(struct net_de
dev->ethtool_ops = &loopback_ethtool_ops;
dev->header_ops = ð_header_ops;
dev->init = loopback_dev_init;
+ dev->open = loopback_dev_start;
+ dev->stop = loopback_dev_stop;
dev->destructor = loopback_dev_free;
}
--- a/include/linux/netdevice.h 2008-11-05 08:18:01.000000000 -0800
+++ b/include/linux/netdevice.h 2008-11-05 08:18:19.000000000 -0800
@@ -366,6 +366,8 @@ static inline int napi_reschedule(struct
return 0;
}
+extern void napi_schedule_irq(struct napi_struct *n);
+
/**
* napi_complete - NAPI processing complete
* @n: napi context
--- a/net/core/dev.c 2008-11-05 08:17:32.000000000 -0800
+++ b/net/core/dev.c 2008-11-05 09:54:36.000000000 -0800
@@ -2369,6 +2369,15 @@ void __napi_schedule(struct napi_struct
}
EXPORT_SYMBOL(__napi_schedule);
+/* Special case version of napi_schedule since loopback device has no hard irq */
+void napi_schedule_irq(struct napi_struct *n)
+{
+ if (napi_schedule_prep(n)) {
+ list_add_tail(&n->poll_list, &__get_cpu_var(softnet_data).poll_list);
+ __raise_softirq_irqoff(NET_RX_SOFTIRQ);
+ }
+}
+
static void net_rx_action(struct softirq_action *h)
{
View attachment "loopback-napi.patch" of type "text/x-patch" (4934 bytes)
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