On Sat, 12 Feb 2005 23:03:18 +0300
Alexey Kuznetsov [off-list ref] wrote:

Actually, that anti-MacOS never worked well. If segment with forced PSH
was not transmitted in time, even forced PSHs could be deleted.
Your patch with setting PSH right before (or in) tcp_transmit_skb() must
work. Unless these segments are not tso.

Yes, it never did work well.  But now we understand more deeply the
nature of this beast, we can probably refine it.

In short, for properly working TCP stream with no drops and no
reordering, Darwin delays ACKs until delack timer fires or PSH
is seen :-)