From: Mina Almasry > Sent: 10 August 2023 02:58 ... > * TL;DR: > > Device memory TCP (devmem TCP) is a proposal for transferring data to and/or > from device memory efficiently, without bouncing the data to a host memory > buffer. Doesn't that really require peer-to-peer PCIe transfers? IIRC these aren't supported by many root hubs and have fundamental flow control and/or TLP credit problems. I'd guess they are also pretty incompatible with IOMMU? I can see how you might manage to transmit frames from some external memory (eg after encryption) but surely processing receive data that way needs the packets be filtered by both IP addresses and port numbers before being redirected to the (presumably limited) external memory. OTOH isn't the kernel going to need to run code before the packet is actually sent and just after it is received? So all you might gain is a bit of latency? And a bit less utilisation of host memory?? But if your system is really limited by cpu-memory bandwidth you need more cache :-) So how much benefit is there over efficient use of host memory bounce buffers?? David - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
