netdev - Re: [PATCH net-next] net: gro: add a per device gro flush timer

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Date:	Wed, 05 Nov 2014 17:38:35 -0800
From:	Rick Jones <rick.jones2@...com>
To:	Eric Dumazet <eric.dumazet@...il.com>,
	David Miller <davem@...emloft.net>
CC:	netdev <netdev@...r.kernel.org>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] net: gro: add a per device gro flush timer

On 11/05/2014 04:55 PM, Eric Dumazet wrote:
> Tested:
>   Ran 200 netperf TCP_STREAM from A to B (10Gbe link, 8 RX queues)
>
> Without this feature, we send back about 305,000 ACK per second.
>
> GRO aggregation ratio is low (811/305 = 2.65 segments per GRO packet)
>
> Setting a timer of 2000 nsec is enough to increase GRO packet sizes
> and reduce number of ACK packets. (811/19.2 = 42)
>
> Receiver performs less calls to upper stacks, less wakes up.
> This also reduces cpu usage on the sender, as it receives less ACK
> packets.
>
> Note that reducing number of wakes up increases cpu efficiency, but can
> decrease QPS, as applications wont have the chance to warmup cpu caches
> doing a partial read of RPC requests/answers if they fit in one skb.

Speaking of QPS, what happens to 200 TCP_RR tests when the feature is 
enabled?

rick jones
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