netdev - Re: Question about LRO/GRO and TCP acknowledgements

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Date:	Sun, 12 Jun 2011 09:51:31 +0200
From:	Joris van Rantwijk <joris@...isvr.nl>
To:	Ben Hutchings <bhutchings@...arflare.com>
Cc:	netdev@...r.kernel.org
Subject: Re: Question about LRO/GRO and TCP acknowledgements

On 2011-06-12, Ben Hutchings <bhutchings@...arflare.com> wrote:
> LRO implementations (and GRO) are expected to put the actual segment
> size in skb_shared_info(skb)->gso_size on the aggregated skb.  TCP
> will then use that rather than the aggregated payload size when
> deciding whether to defer an ACK.

Thanks. I see that indeed gso_size is being used for MSS calculations
instead of the total GRO size.

However, I'm not sure that this completely answers my question.
I am not so much concerned about quick ACK vs delayed ACK.
Instead, I'm looking at the total number of ACKs transmitted.
The sender depends on the _number_ of ACKs to update its congestion
window.

As far as I can see, current code will send just one ACK per coalesced
GRO bundle, while the sender expects one ACK per two segments.

Thanks,
Joris.
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