Re: [PATCH net-next] net: gro: change GRO overflow strategy

[David Miller <davem@davemloft.net>]

From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 09 Jan 2014 14:12:19 -0800

> From: Eric Dumazet <edumazet@google.com>
> 
> GRO layer has a limit of 8 flows being held in GRO list,
> for performance reason.
> 
> When a packet comes for a flow not yet in the list,
> and list is full, we immediately give it to upper
> stacks, lowering aggregation performance.
> 
> With TSO auto sizing and FQ packet scheduler, this situation
> happens more often.
> 
> This patch changes strategy to simply evict the oldest flow of
> the list. This works better because of the nature of packet
> trains for which GRO is efficient. This also has the effect
> of lowering the GRO latency if many flows are competing.
> 
> Tested :
> 
> Used a 40Gbps NIC, with 4 RX queues, and 200 concurrent TCP_STREAM
> netperf.
> 
> Before patch, aggregate rate is 11Gbps (while a single flow can reach
> 30Gbps)
> 
> After patch, line rate is reached.
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, looks great.

If someone is really concerned about improving the list traversal,
we can maintain a tail pointer.