On Tue, Nov 24, 2009 at 05:23, Eric Dumazet [off-list ref] wrote:

Here is an updated version, because ixgbe_get_ethtool_stats()
needs to call dev_get_stats() or "ethtool -S" wont give
correct tx_bytes/tx_packets values.

[PATCH net-next-2.6] ixgbe: Fix TX stats accounting

Several cpus can update netdev->stats.tx_bytes & netdev->stats.tx_packets
in parallel. In this case, TX stats are under estimated and false sharing
takes place.

After a pktgen session sending exactly 200000000 packets :
# ifconfig fiber0 | grep TX
         TX packets:198501982 errors:0 dropped:0 overruns:0 carrier:0


Multi queue devices should instead use txq->tx_bytes & txq->tx_packets
in their xmit() method (appropriate txq lock already held by caller, no
cache line miss), or use appropriate locking.

After patch, same pktgen session gives :

# ifconfig fiber0 | grep TX
         TX packets:200000000 errors:0 dropped:0 overruns:0 carrier:0

Signed-off-by: Eric Dumazet <redacted>
---
 drivers/net/ixgbe/ixgbe_ethtool.c |    1 +
 drivers/net/ixgbe/ixgbe_main.c    |   20 ++++----------------
 2 files changed, 5 insertions(+), 16 deletions(-)

Thanks Eric.  I have added the patch to my tree for testing and review.

-- 
Cheers,
Jeff