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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>
This commit is contained in:
Eric Dumazet 2009-05-18 00:34:33 +00:00 committed by David S. Miller
parent ba98898eb3
commit 7004bf252c
2 changed files with 23 additions and 3 deletions
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3
include/linux/netdevice.h
View File

@ -474,6 +474,9 @@ struct netdev_queue {
* 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;

23
net/core/dev.c
View File

@ -4943,13 +4943,30 @@ void netdev_run_todo(void)
* 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);