Hello!

quoted

In some cases at least if the sender does not completely fill cwnd the
ACKs will  be delayed.  And IIRC under 2.6.10 with TSO enabled, the
sender does not always  fill cwnd.

At a maximum, "1/tcp_tso_win_divisor" of the cwnd will ever be left
empty.

By default, this is 1/8 of the cwnd.

In any case, receiver cannot know sender cwnd, so that "fill" or "not fill"
is is not a question.

What is broken in that implementation is that it does not feel slow start.
ACK avoidance while slow start is certain disaster. Currrent theory is that
MacOS X thinks that we do not do slow start.

Alexey