I agree about the polynomial. That would have been nice. As currently proposed the embedding of the IB transport in Ethernet frames preserves the IB ICRC as part of the transport and trades the VCRC for Ethernet's CRC32 over the whole frame. This means that the packet is effectively covered by CRC32 twice except for the 802 headers and the fields that are excluded from the ICRC. CRC32C should give better protection.
We have thought that we could try CRC32C first and if that works then use that, otherwise fall back to CRC32 which would allow rxe to use CRC32C when talking to itself and get a speedup on new Intel CPUs. The crc32 code we have is based on some suggestions from Intel and seems to be much faster than the 'standard' code in the kernel and we are/were planning to merge the crc computation with the data copy. It is actually less explicitly optimized than the code in the kernel but when we use the loop unrolling directive in the compiler we get better overall results. That core loop gives us about 5-6GB/sec for the copy/crc vs about 500MB/sec for the 'standard' crc + copy. Our plan is to strip out all the trace and dump code when the driver is stable. We will keep the warn and error messages. Bob -----Original Message----- From: Roland Dreier [mailto:rdre...@cisco.com] Sent: Thursday, December 17, 2009 3:26 PM To: Robert Pearson Cc: 'Jason Gunthorpe'; 'frank zago'; linux-rdma@vger.kernel.org; 'John Groves' Subject: Re: [Announce] rxe dev tree available (soft RDMAoE) > Yes, but later. For now it is still being actively developed and is changing > a lot. Once it settles down we plan to convert to patches and push up > stream. I think you would probably be better off developing the kernel driver as a branch in an up-to-date kernel tree, and then worrying about backports later. You could get rid of some of the redundant infrastructure like dump_hex() and crc32 (too bad IB didn't choose the CRC32C polynomial, so you can't use the crypto API and get Intel CRC32 instruction acceleration for free). - R. -- To unsubscribe from this list: send the line "unsubscribe linux-rdma" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
