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

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Date:	Tue, 24 Nov 2009 23:38:23 -0800
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Peter P Waskiewicz Jr <peter.p.waskiewicz.jr@...el.com>,
	"robert@...julf.net" <robert@...julf.net>,
	Jesper Dangaard Brouer <hawk@...u.dk>,
	Linux Netdev List <netdev@...r.kernel.org>,
	"David S. Miller" <davem@...emloft.net>
Subject: Re: [PATCH net-next-2.6] ixgbe: Fix TX stats accounting

On Tue, Nov 24, 2009 at 05:23, Eric Dumazet <eric.dumazet@...il.com> 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 <eric.dumazet@...il.com>
> ---
>  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
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