On 12/7/20 2:06 PM, Boris Pismenny wrote: > This commit introduces direct data placement offload for TCP. > This capability is accompanied by new net_device operations that > configure > hardware contexts. There is a context per socket, and a context per DDP > opreation. Additionally, a resynchronization routine is used to assist > hardware handle TCP OOO, and continue the offload. > Furthermore, we let the offloading driver advertise what is the max hw > sectors/segments. > > Using this interface, the NIC hardware will scatter TCP payload directly > to the BIO pages according to the command_id. > To maintain the correctness of the network stack, the driver is expected > to construct SKBs that point to the BIO pages. > > This, the SKB represents the data on the wire, while it is pointing > to data that is already placed in the destination buffer. > As a result, data from page frags should not be copied out to > the linear part. > > As SKBs that use DDP are already very memory efficient, we modify > skb_condence to avoid copying data from fragments to the linear > part of SKBs that belong to a socket that uses DDP offload. > > A follow-up patch will use this interface for DDP in NVMe-TCP. >
You call this Direct Data Placement - which sounds like a marketing name. Fundamentally, this starts with offloading TCP socket buffers for a specific flow, so generically a TCP Rx zerocopy for kernel stack managed sockets (as opposed to AF_XDP's zerocopy). Why is this not building in that level of infrastructure first and adding ULPs like NVME on top?
