[openib-general] [PATCH][iWARP] Added provider CM verbsandquery provider methods

[Gleb Natapov]

On Tue, Aug 30, 2005 at 12:00:42PM -0700, Caitlin Bestler wrote:
> > > TOE for the purposes of RDMA may have more legs within the 
> > community, 
> > > however, this has yet to be tested.
> > Is it possible to implement RDMA semantics using linux native 
> > TCP stack (with hardware assistance of cause)? Just asking.
> > 
> > 
> 
> It is possible to implement RDMA on the host processor. But
> it will not match the performance of hardware. The difference
> will be substantial at 10G. If someobody could build a software
> only solution that performed at 10G they would have done so.
> Having zero manufacturing cost would give them quite a 
> competitive edge over solutions that required hardware.
> 
I am not talking about software only solution. Hardware assistance
is needed, but something less then TOE. Something stateless like
Dave wants.

> The need for offload has more to do with memory bandwidth
> than raw processing power. The data bandwidth required to
> support look-up of large data structures and for placement
> of the raw payload nearly consumes the bus bandwidth when
> operating at peak wire speeds. If you make that worse by
> moving the raw packets over the wire, and *then* copying
> them to a final location (a second memory move) *and*
> additional memory touches for accessing control structures...
> 
Linux already have the infrastructure for zero-copy send, with
some hardware help it is possible to implement zero-copy receive too.
Moving data in memory is out of the question.

Anyway I think this questions should be answered before moving this
discussion to netdev.

--
			Gleb.