netdev - Re: LRO/GRO and libpcap packet reordering

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Date:	Thu, 14 Mar 2013 16:22:43 -0700
From:	Andy Lutomirski <luto@...capital.net>
To:	Eric Dumazet <eric.dumazet@...il.com>
Cc:	Ben Hutchings <bhutchings@...arflare.com>,
	Network Development <netdev@...r.kernel.org>
Subject: Re: LRO/GRO and libpcap packet reordering

On Thu, Mar 14, 2013 at 4:21 PM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> On Fri, 2013-03-15 at 00:16 +0100, Eric Dumazet wrote:
>> On Thu, 2013-03-14 at 15:58 -0700, Andy Lutomirski wrote:
>>
>> > Right.  This is the part that I'm wondering about an efficient fix to
>> > (i.e. flush GRO state for one flow whenever a packet for the reversed
>> > flow is seen).
>>
>> It doesnt seem doable easily, because network header and tcp headers are
>> handled in two separate functions in GRO stack (inet_gro_receive() &
>> tcp_gro_receive()
>>
>> What you could do is changing MAX_GRO_SKBS from 8 to 1
>> (basically allowing only one flow in GRO stack)
>>
>>
> Well, its not enough, some changes would be needed to force a flush each
> time a new flow is detected.
>
>
>

Hmm.  Maybe a better "fix" would be to have some up-to-date
documentation or other indication of what needs to happen to get clean
packet captures.  I'm not sure where it should go.

--Andy

-- 
Andy Lutomirski
AMA Capital Management, LLC
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