We see a performance problem when the slaves of the bond don't support checksum offload features. What we see is tcp_sendmsg's skb_add_data_nocache ending up not using the csum_and_copy_from_user which would have computed the checksum while copying from user buffer to kernel buffer. Instead it computes later in dev_hard_start_xmit when it figures out the slave doesn't support checksum offload and ends up expensive .
The bonding interface's "features" has NETIF_F_HW_CSUM (or NETIF_F_NO_CSUM in 2.6.39) set which makes the stack think checksum need not be computed in software. /* * Check whether we can use HW checksum. */ if (sk->sk_route_caps & NETIF_F_ALL_CSUM) skb->ip_summed = CHECKSUM_PARTIAL; But later in dev_hard_start_xmit it finds out the slave does not support checksumming and decides to compute in software. /* If packet is not checksummed and device does not * support checksumming for this protocol, complete * checksumming here. */ if (skb->ip_summed == CHECKSUM_PARTIAL) { skb_set_transport_header(skb, skb_checksum_start_offset(skb)); if (!(features & NETIF_F_ALL_CSUM) && skb_checksum_help(skb)) goto out_kfree_skb; } We see this problem after this commit: commit 1742f183fc218798dab6fcf0ded25b6608fc0a48 Author: MichaÅ<82> MirosÅ<82>aw <mirq-li...@rere.qmqm.pl> Date: Fri Apr 22 06:31:16 2011 +0000 net: fix netdev_increment_features() Simplify and fix netdev_increment_features() to conform to what is stated in netdevice.h comments about NETIF_F_ONE_FOR_ALL. Include FCoE segmentation and VLAN-challedged flags in computation. Signed-off-by: MichaÅ<82> MirosÅ<82>aw <mirq-li...@rere.qmqm.pl> Signed-off-by: David S. Miller <da...@davemloft.net> Prior to that the below code in netdev_increment_features was helping in turning off NETIF_F_NO_CSUM on bond when the slaves don't support it: /* If device needs checksumming, downgrade to it. */ if (all & NETIF_F_NO_CSUM && !(one & NETIF_F_NO_CSUM)) all ^= NETIF_F_NO_CSUM | (one & NETIF_F_ALL_CSUM); The slaves are Mellanox IB adapters. This is on x86_64 platform. Please let us know if you need any additional information. Thanks. Venkat -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/