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snabbco / snabb

Snabb: Simple and fast packet networking
Apache License 2.0
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Zero-copy in most NICs? #1447

Open gorgonical opened 5 years ago

gorgonical commented 5 years ago

I couldn't find anything in the docs or the code that confirmed this question, so I figured I would ask. I would have asked in the Slack but the invite link is broken.

Does Snabb provide zero-copy semantics for NICs? I know that the memory module provides DMA memory for the NIC to access and the usage in some parts of the code such as:

src/apps/intel_mp/intel_mp.lua:555:   memory.dma_alloc(ffi.sizeof(rxdesc_ring_t)))
src/apps/intel_mp/intel_mp.lua:625:   memory.dma_alloc(ffi.sizeof(txdesc_ring_t)))

indicate that the DMA memory is being used for the NIC queues, but I wanted to be sure.

eugeneia commented 5 years ago

Yes, that is what we do. I.e., let the hardware write to and read from our struct packet buffers in DMA memory directly.

https://github.com/lukego/blog/issues/13 might give slightly more detail from the OS perspective.

eugeneia commented 5 years ago

The invite link should work again btw. :-)