[PATCH] [NET] reduce per cpu ram used for loopback stats

[Eric Dumazet]

We dont need a full struct net_device_stats (currently 23 long : 184 bytes on 
x86_64) per possible CPU, but only two counters : bytes and packets

We save few CPU cycles too in loopback_xmit() not updating 4 fields, but 2. 

Signed-off-by: Eric Dumazet <[EMAIL PROTECTED]>

--- linux/drivers/net/loopback.c        2006-10-18 17:28:20.000000000 +0200
+++ linux-eddrivers/net/loopback.c      2006-10-18 18:26:41.000000000 +0200
@@ -58,7 +58,11 @@
 #include <linux/tcp.h>
 #include <linux/percpu.h>
 
-static DEFINE_PER_CPU(struct net_device_stats, loopback_stats);
+struct pcpu_lstats {
+       unsigned long packets;
+       unsigned long bytes;
+};
+static DEFINE_PER_CPU(struct pcpu_lstats, pcpu_lstats);
 
 #define LOOPBACK_OVERHEAD (128 + MAX_HEADER + 16 + 16)
 
@@ -128,7 +132,7 @@
  */
 static int loopback_xmit(struct sk_buff *skb, struct net_device *dev)
 {
-       struct net_device_stats *lb_stats;
+       struct pcpu_lstats *lb_stats;
 
        skb_orphan(skb);
 
@@ -149,11 +153,9 @@
 #endif
        dev->last_rx = jiffies;
 
-       lb_stats = &per_cpu(loopback_stats, get_cpu());
-       lb_stats->rx_bytes += skb->len;
-       lb_stats->tx_bytes = lb_stats->rx_bytes;
-       lb_stats->rx_packets++;
-       lb_stats->tx_packets = lb_stats->rx_packets;
+       lb_stats = &per_cpu(pcpu_lstats, get_cpu());
+       lb_stats->bytes += skb->len;
+       lb_stats->packets++;
        put_cpu();
 
        netif_rx(skb);
@@ -166,20 +168,21 @@
 static struct net_device_stats *get_stats(struct net_device *dev)
 {
        struct net_device_stats *stats = &loopback_stats;
+       unsigned long bytes = 0;
+       unsigned long packets = 0;
        int i;
 
-       memset(stats, 0, sizeof(struct net_device_stats));
-
        for_each_possible_cpu(i) {
-               struct net_device_stats *lb_stats;
+               const struct pcpu_lstats *lb_stats;
 
-               lb_stats = &per_cpu(loopback_stats, i);
-               stats->rx_bytes   += lb_stats->rx_bytes;
-               stats->tx_bytes   += lb_stats->tx_bytes;
-               stats->rx_packets += lb_stats->rx_packets;
-               stats->tx_packets += lb_stats->tx_packets;
+               lb_stats = &per_cpu(pcpu_lstats, i);
+               bytes   += lb_stats->bytes;
+               packets += lb_stats->packets;
        }
-
+       stats->rx_packets = packets;
+       stats->tx_packets = packets;
+       stats->rx_bytes = bytes;
+       stats->tx_bytes = bytes;
        return stats;
 }