netdev - Re: LRO/GRO and libpcap packet reordering

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Message-ID: <1363301695.29475.38.camel@edumazet-glaptop>
Date:	Thu, 14 Mar 2013 23:54:55 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Andy Lutomirski <luto@...capital.net>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: LRO/GRO and libpcap packet reordering

On Thu, 2013-03-14 at 15:45 -0700, Andy Lutomirski wrote:

> Hmm.  What if the GRO flow hashing was something like hash(one
> endpoint) ^ hash(the other endpoint)?  (NB: I don't really know what
> I'm talking about.)

There is no hashing in GRO, but a full flow match.

What you describe has to do with multi queue capability of the NIC.

Each flow is handled by a separate RX queue, therefore by different
cpus. There is no guarantee packets are delivered 'in order' in this
case, GRO being off or on.

Of course, if GRO/LRO is on, there is an additional delay to permit
aggregation, so a big GRO/LRO packet might appear _after_ an ACK.

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