Is it possible to get an RDMA adapter (e.g. Mellanox NIC) to do an endian conversion during data transfer? Specifically, we're doing an RDMA transfer from a big-endian to a little-endian system and vice versa. Once data lands at the target, then we need to do a bswap32() or bswap64() to do the endian conversion which will chew processor cycles. I am wondering if we can get free bswaps from the NIC instead.
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Swapping endianness is not an operation/attribute that is defined in the InfiniBand spec. However, Mellanox devices (ConnectX-4 and up) do provide look-aside vector calculation primitives, with endianity swap as one of the operations supported. This essentially means that one may be able to perform this look-aside HW swap on the data before sending it or after receiving it.
This vector calculation capability is still in its early stages in terms of exposure to higher-level APIs. You will be able to find some references in these Linux kernel commits:
- https://patchwork.kernel.org/patch/8365791/ ([rdma-next,3/8] net/mlx5_core: Introduce offload arithmetic hardware capabilities)
- https://patchwork.kernel.org/patch/8388951/ ([rdma-next,V1,7/8] IB/core: Advertise supported vector CALC capabilities)
Partial support is also available through the "experimental verbs" on Mellanox OFED - keep watching for updates to come.
Yuval Degani
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