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

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Date:	Tue, 14 Jun 2011 21:37:18 +0200
From:	Joris van Rantwijk <joris@...isvr.nl>
To:	"Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi>
Cc:	Netdev <netdev@...r.kernel.org>
Subject: Re: Question about LRO/GRO and TCP acknowledgements

On 2011-06-14, "Ilpo Järvinen" <ilpo.jarvinen@...sinki.fi> wrote:
> BTW, it wouldn't be impossible to create all those "missing" ACKs on
> the TCP layer relatively cheaply when receiving the GRO'ed super
> segment.  I'm certainly not opposed you coming up such patch which
> does all that minimal work needed on TCP layer but I think it
> requires also some TSO/GSO related problem solving because TSO/GSO as
> is won't let you create such super ACKs we'd want to send out on that
> single go.

Your super-ACK idea is similar to the solution presented in this paper:
http://www.usenix.org/event/usenix08/tech/full_papers/menon/menon_html/

Actually, I started looking at the GRO code after reading that
paper, hoping to find that Linux has a better way to deal with ACKs.

The super ACK doesn't look easy. It must contain all different ack_seq
values to avoid tripping duplicate ACK detection. Ideally, the ack_seq
values would match real seq values from the received segments.

I don't currently have a setup where I could test these kinds of
changes, so this doesn't seem like a job for me. At least not right now.

Thanks, Joris.
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