When drivers have support for offloading transport IP checksums, they will indicate this in the features for the device. As described in skbuff.h, a driver will usually advertise NETIF_F_HW_CSUM, NETIF_F_IP_CSUM, and/or NETIF_F_IPV6_CSUM. The first of these (NETIF_F_HW_CSUM) is the preferred method since this implies that the device has implemented a generic checksum offload feature that should work under arbitrary scenarios (e.g. for different protocols, with or without encapsulation).
For narrow features support (NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM for offload of TCP/UDP), the features flags may not be sufficient to deduce whether a packet may be offloaded. Some devices will not be able to offload encapsulated checksums, some cannot offload transport checksums in packet with IPv6 extension headers, etc. In these cases a driver will need to perform additional packet inspection to determine if a packet's checksum can be offloaded to a device. This patch defines a helper function that drivers can call to check if it is able to offload the checksum for a particular packet. In an argument to the function, the driver specifies what type of packets it is able to offload to a device. The function is intended to check for the most common restrictions of devices (like by IP version, transport protocol, encapsulation, extension headers). Since the function includes checks for IP version and transport protocol, the driver is able to advertise NETIF_F_HW_CSUM instead of protocol specific support. This should put us on a path to deprecate NETIF_F_IP_CSUM and NETIF_F_IPV6_CSUM. The helper function may be called from ndo_features_check or the xmit routine of the driver. The csum_help argument does not need to be set when the function is called from ndo_features_check. Note that the helper function is intended to verify checksum offloadability in the non-LSO case. Checksum offload as part of LSO should be validated as part of GSO offload checks (through NETIF_F_GSO_* flags and work done in ndo_features_check). In this patch set: - Added skb_csum_offload_chk function - Call skb_csum_offload_chk from mlx4 Testing: Ran 200 netperf TCP_RR to see impact of calling skb_csum_offload_chk for every packet. Did not observe any noticeable regression. Perf shows that the function was 0.20% utilization which puts it pretty far down the list. Tom Herbert (3): net: Add skb_inner_transport_offset function net: Add driver helper function to determine checksum offloadability mlx4: Call skb_csum_offload_check to check offloadability drivers/net/ethernet/mellanox/mlx4/en_netdev.c | 6 +- drivers/net/ethernet/mellanox/mlx4/en_tx.c | 20 +++- include/linux/netdevice.h | 47 +++++++++ include/linux/skbuff.h | 5 + net/core/dev.c | 129 +++++++++++++++++++++++++ 5 files changed, 199 insertions(+), 8 deletions(-) -- 2.4.6 -- To unsubscribe from this list: send the line "unsubscribe netdev" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
