From: Simon Horman <ho...@verge.net.au> Date: Mon, 20 May 2013 10:46:49 +0900
> This is a generic solution to resolve a specific problem that I have observed. > > If the encapsulation of an skb changes then ability to offload checksums > may also change. In particular it may be necessary to perform checksumming > in software. > > An example of such a case is where a non-GRE packet is received but > is to be encapsulated and transmitted as GRE. > > Another example relates to my proposed support for for packets > that are non-MPLS when received but MPLS when transmitted. > > The cost of this change is that the value of the csum variable may be > checked when it previously was not. In the case where the csum variable is > true this is pure overhead. In the case where the csum variable is false it > leads to software checksumming, which I believe also leads to correct > checksums in transmitted packets for the cases described above. > > Further analysis: > > This patch relies on the return value of can_checksum_protocol() > being correct and in turn the return value of skb_network_protocol(), > used to provide the protocol parameter of can_checksum_protocol(), > being correct. It also relies on the features passed to skb_segment() > and in turn to can_checksum_protocol() being correct. > > I believe that this problem has not been observed for VLANs because it > appears that almost all drivers, the exception being xgbe, set > vlan_features such that that the checksum offload support for VLAN packets > is greater than or equal to that of non-VLAN packets. > > I wonder if the code in xgbe may be an oversight and the hardware does > support checksumming of VLAN packets. If so it may be worth updating the > vlan_features of the driver as this patch will force such checksums to be > performed in software rather than hardware. > > Signed-off-by: Simon Horman <ho...@verge.net.au> Applied, thanks Simon. _______________________________________________ dev mailing list dev@openvswitch.org http://openvswitch.org/mailman/listinfo/dev
