netdev - Re: [E1000-devel] [PATCH net 2/2] net: core: explicitly select a txq before doing l2 forwarding

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Date:	Mon, 06 Jan 2014 04:04:50 -0800
From:	Jeff Kirsher <jeffrey.t.kirsher@...el.com>
To:	Jason Wang <jasowang@...hat.com>, aaron.f.brown@...el.com
Cc:	davem@...emloft.net, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	John Fastabend <john.r.fastabend@...el.com>,
	e1000-devel@...ts.sourceforge.net,
	Neil Horman <nhorman@...driver.com>, mst@...hat.com
Subject: Re: [E1000-devel] [PATCH net 2/2] net: core: explicitly select a
 txq before doing l2 forwarding

On Mon, 2014-01-06 at 11:21 +0800, Jason Wang wrote:
> Currently, the tx queue were selected implicitly in
> ndo_dfwd_start_xmit(). The
> will cause several issues:
> 
> - NETIF_F_LLTX was forced for macvlan device in this case which lead
> extra lock
>   contention.
> - dev_hard_start_xmit() was called with NULL txq which bypasses the
> net device
>   watchdog
> - dev_hard_start_xmit() does not check txq everywhere which will lead
> a crash
>   when tso is disabled for lower device.
> 
> Fix this by explicitly introducing a select queue method just for l2
> forwarding
> offload (ndo_dfwd_select_queue), and introducing dfwd_direct_xmit() to
> do the
> queue selecting and transmitting for l2 forwarding.
> 
> With this fixes, NETIF_F_LLTX could be preserved for macvlan and
> there's no need
> to check txq against NULL in dev_hard_start_xmit().
> 
> In the future, it was also required for macvtap l2 forwarding support
> since it
> provides a necessary synchronization method.
> 
> Cc: John Fastabend <john.r.fastabend@...el.com>
> Cc: Neil Horman <nhorman@...driver.com>
> Cc: e1000-devel@...ts.sourceforge.net
> Signed-off-by: Jason Wang <jasowang@...hat.com>
> ---
>  drivers/net/ethernet/intel/ixgbe/ixgbe_main.c |   15 +++++++++----
>  drivers/net/macvlan.c                         |    3 +-
>  include/linux/netdevice.h                     |   11 +++++++++
>  net/core/dev.c                                |   28
> ++++++++++++++++++++++++-
>  4 files changed, 49 insertions(+), 8 deletions(-)

Thanks Jason, I have added this to my queue since it has changes against
ixgbe.

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