net: add tx_packets/tx_bytes/tx_dropped counters in struct netdev_queue
offsetof(struct net_device, features)=0x44
offsetof(struct net_device, stats.tx_packets)=0x54
offsetof(struct net_device, stats.tx_bytes)=0x5c
offsetof(struct net_device, stats.tx_dropped)=0x6c
Network drivers that touch dev->stats.tx_packets/stats.tx_bytes in their
tx path can slow down SMP operations, since they dirty a cache line
that should stay shared (dev->features is needed in rx and tx paths)
We could move away stats field in net_device but it wont help that much.
(Two cache lines dirtied in tx path, we can do one only)
Better solution is to add tx_packets/tx_bytes/tx_dropped in struct
netdev_queue because this structure is already touched in tx path and
counters updates will then be free (no increase in size)
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index cd547d0..f8574e7 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -474,6 +474,9 @@
* please use this field instead of dev->trans_start
*/
unsigned long trans_start;
+ unsigned long tx_bytes;
+ unsigned long tx_packets;
+ unsigned long tx_dropped;
} ____cacheline_aligned_in_smp;
diff --git a/net/core/dev.c b/net/core/dev.c
index 14dd725..6d3630d 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -4943,13 +4943,30 @@
* the internal statistics structure is used.
*/
const struct net_device_stats *dev_get_stats(struct net_device *dev)
- {
+{
const struct net_device_ops *ops = dev->netdev_ops;
if (ops->ndo_get_stats)
return ops->ndo_get_stats(dev);
- else
- return &dev->stats;
+ else {
+ unsigned long tx_bytes = 0, tx_packets = 0, tx_dropped = 0;
+ struct net_device_stats *stats = &dev->stats;
+ unsigned int i;
+ struct netdev_queue *txq;
+
+ for (i = 0; i < dev->num_tx_queues; i++) {
+ txq = netdev_get_tx_queue(dev, i);
+ tx_bytes += txq->tx_bytes;
+ tx_packets += txq->tx_packets;
+ tx_dropped += txq->tx_dropped;
+ }
+ if (tx_bytes || tx_packets || tx_dropped) {
+ stats->tx_bytes = tx_bytes;
+ stats->tx_packets = tx_packets;
+ stats->tx_dropped = tx_dropped;
+ }
+ return stats;
+ }
}
EXPORT_SYMBOL(dev_get_stats);
