net: add tx_packets/tx_bytes/tx_dropped counters in struct netdev_queue (7004bf25) · Commits · 戴 / test

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>

include/linux/netdevice.h

+3 −0

Original line number	Diff line number	Diff line
		@@ -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;

net/core/dev.c

+20 −3

Original line number	Diff line number	Diff line
		@@ -4948,8 +4948,25 @@ const struct net_device_stats dev_get_stats(struct net_device dev)

		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);

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