On Sun, Nov 03, 2013 at 08:28:24AM -0800, Eric Dumazet wrote:

1) Because we should not call skb_segment() at all on a router ?

2) If you aggregate too much on a router, you increase latencies,
   or if you prefer the RTT of TCP flows.

3) Because skb_segment() layer only builds MSS sized skb, so this
   remove TSO ability on output path

Splitting a 45 MSS packet into 3 TSO packets (16 + 16 + X MSS) is going
to be quite complex, given the gso_segment() stuff is meant to segment
in MSS packets. Adding complexity in this already complex stuff is
simply not worth it.

For local TCP, its different, because if you receive such high
throughput, ability to build full size GRO packet helps to reduce number
of ACK segments and number of SKB in receive queue (or OFO queue),
without impacting ACK clocking and TCP dynamics.

And even if a router does not do this aggregation, the final receiver
will do.

So in conclusion, GRO is like TSO : Its not because they are able to use
64KB skbs you always _have_ to fill skb to max capacity.

I give up.  It's as if you've ignored everything I've said before.
-- 
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