Hi, Le jeudi 30 juillet 2015 à 04:46 -0700, Yuval Shaia a écrit : > This enhancement suggest the usage of IB CRC instead of CSUM in IPoIB > CM. IPoIB CM uses RC (Reliable Connection) which guarantees the > corruption free delivery of the packet. > > InfiniBand uses 32b CRC which provides stronger data integrity > protection compare to 16b IP Checksum. InfiniBand 32b CRC <=> Ethernet 32b CRC, it's link layer, layer 2. IPv4 checksum is at another level, it's internet layer, layer 3. > So, there is no added value that IP/TCP Checksum provides in the IB > world. > Sure, IPv4 checksum is a thing of the past: checksum was dropped from IP header in IPv6: it assumes the lower layer, such as Ethernet, provides the required integrety check. I think not checking the IPv4 checksum should be a choice, carefully thought, for inside a fabric, as I understand your proposal, packet with invalid checksum will be allowed to go in/out of the fabric. It sound like it's a departure from the behavior one can expect from an IPv4 network stack. > The proposal is to tell network stack that IPoIB-CM supports IP > Checksum offload. This enables the kernel to save the time of > checksum calculation of IPoIB CM packets. Network sends the IP packet > without adding the IP Checksum to the header. On the receive side, > IPoIB driver again tells the network stack that IP Checksum is good > for the incoming packets and network stack avoids the IP Checksum > calculations. > > During connection establishment the driver determine if peer supports > IB CRC as checksum. This is done so driver will be able to calculate > checksum before transmiting the packet in case the peer does not > support this feature. > Two questions: - What will see tool such as wireshark/tcpdump when sniffing checksum -less IPv4 packets sent/received on IPoIB interface ? - What might happen if such checksum-less IPv4 packet is later routed to a different IPv4 network ? > With this enhancement throughput is increased by 60%. > > Signed-off-by: Yuval Shaia <yuval.shaia@xxxxxxxxxx> Regards. -- Yann Droneaud OPTEYA -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
