Whether tracked as bytes or segments, my take is that to ask 
applications to have to think about another non-portable socket option 
is ungood.  I would suggest taking the time to work-out the automagic 
heuristic to drop the deferred ACK count on connections where it being 
large is un-desirable and then not need to worry about the limits being 
global.

Given the stack's existing propensity to try to decide when to increase 
the window I might even go so far as to suggest the sense of the 
heuristic be flipped and it seek to decide when it is ok to increase the 
number of segments/bytes per ACK.  To what extent one needs to go beyond 
what happens already with the stretching of ACKs via GRO/LRO or if that 
mechanism can serve as part of the logic of the heuristic is probably a 
fertile area for discussion.

If I recall correctly, in one of your earlier posts you mentioned 
something about a 20% performance boost.  What were the specific 
conditions of that testing?  Was it over a setup where the receiver 
already had LRO/GRO or was it over a more plain receiver NIC without 
that functionality?

rick jones