[openib-general] Re: [Rdma-developers] Meeting (07/22)summary:OpenRDMA community development discussion

[Tom Tucker]

'Christoph Hellwig' wrote:

>>Can you provide more details on exactly why you think this is a horrible
>>idea?  I agree it will be complex, but it _could_ be scoped such that the
>>complexity is reduced.  For instance, the "offload" function could fail
>>(with EBUSY or something) if there is _any_ data pending on the socket.
>>Thus removing any requirement to pass down pending unacked outgoing data, or
>>pending data that has been received but not yet "read" by the application.
>>The idea here is that the applications at the top "know" they are going into
>>RDMA mode and have effectively quiesced the connection before attempting to
>>move the connection into RDMA mode.  We could, in fact, _require_ the
>>connect be quiesced to keep things simpler.  I'm quickly sinking into gory
>>details, but I want to know if you have other reasons (other than the
>>complextity) for why this is a bad idea.
>>    
>>
>
>I think your writeup here is more than explanation enough.  The offload
>can only work for few special cases, and even for those it's rather
>complicated, especially if you take things as ipsec or complex tunneling
>that get more and more common into account.  
>
I think Steve's point was that it *can* be simplified as necessary to 
meet the demands/needs of the Linux community. It is certainly 
technically possible, but agreeably complicated to offload an active socket.

>What do you archive by
>implementing the offload except trying to make it look more integrated
>to the user than it actually is?  Just offload rmda protocols to the
>RDMA hardware and keep the IP stack out of that complexity.
>
You get the benefit of things like SYN flood DOS attack avoidance built 
into the host stack without replicating this functionality in the 
offloaded adapter. There are other benefits of integration like 
failover, etc... IMHO, however, the bulk of the benefits are for ULP 
offload like RDMA where the remote peer may not be capable of HW RDMA 
acceleration. This kind of thing could be determined in "streaming mode" 
using the host stack and then migrated to an adapter for HW acceleration 
only if the remote peer is capable.

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