Selective signalling vs WQE size - was Re: [ofa-general] mthca max_sge value... ugh.

[Roland Dreier]

 > Roland, I posted a few months ago a patch that optimizes post send for
 > selective signaling QPs. It must have slipped somehow because I did not
 > get any reply on it and since I did not know of anyone using selective
 > signaling I forgot about this too. The idea is that for selective
 > signaling QPs, before you stamp the WQE, you read the value of the DS
 > field which denotes the effective size of the descriptor as used in the
 > previous post, and stamp only that area, relying on the fact that the
 > rest of the descriptor is already stamped. Here is a link to the patch.
 > I don't know if it applies cleanly now but if we agree on the idea I
 > will generate it again against the current tree.

Does it make a measurable difference?  If so then it seems like a good idea.