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SubjectRe: [PATCH net V3 2/2] net: core: explicitly select a txq before doing l2 forwarding
On Fri, Jan 10, 2014 at 04:18:26PM +0800, Jason Wang wrote:
> Currently, the tx queue were selected implicitly in ndo_dfwd_start_xmit(). The
> will cause several issues:
>
> - NETIF_F_LLTX were removed for macvlan, so txq lock were done for macvlan
> instead of lower device which misses the necessary txq synchronization for
> lower device such as txq stopping or frozen required by dev watchdog or
> control path.
> - 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 new param for .ndo_select_queue() for just
> selecting queues in the case of l2 forwarding offload. netdev_pick_tx() was also
> extended to accept this parameter and dev_queue_xmit_accel() was used to do l2
> forwarding transmission.
>
> 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(). Also there's no need to keep
> a dedicated ndo_dfwd_start_xmit() and we can just reuse the code of
> dev_queue_xmit() to do the transmission.
>
> 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@intel.com>
> Cc: Neil Horman <nhorman@tuxdriver.com>
> Cc: e1000-devel@lists.sourceforge.net
> Signed-off-by: Jason Wang <jasowang@redhat.com>
>
Acked-by: Neil Horman <nhorman@tuxdriver.com>



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