netdev - Re: [PATCH net-next] netem: Introduce skb_orphan

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Message-Id: <20130731.150020.1079928001574422468.davem@davemloft.net>
Date:	Wed, 31 Jul 2013 15:00:20 -0700 (PDT)
From:	David Miller <davem@...emloft.net>
To:	eric.dumazet@...il.com
Cc:	netdev@...r.kernel.org
Subject: Re: [PATCH net-next] netem: Introduce skb_orphan_partial() helper

From: Eric Dumazet <eric.dumazet@...il.com>
Date: Tue, 30 Jul 2013 17:55:08 -0700

> From: Eric Dumazet <edumazet@...gle.com>
> 
> Commit 547669d483e578 ("tcp: xps: fix reordering issues") added
> unexpected reorders in case netem is used in a MQ setup for high
> performance test bed.
> 
> ETH=eth0
> tc qd del dev $ETH root 2>/dev/null
> tc qd add dev $ETH root handle 1: mq
> for i in `seq 1 32`
> do
>  tc qd add dev $ETH parent 1:$i netem delay 100ms
> done
> 
> As all tcp packets are orphaned by netem, TCP stack believes it can
> set skb->ooo_okay on all packets.
> 
> In order to allow producers to send more packets, we want to 
> keep sk_wmem_alloc from reaching sk_sndbuf limit.
> 
> We can do that by accounting one byte per skb in netem queues,
> so that TCP stack is not fooled too much.
 ...
> Signed-off-by: Eric Dumazet <edumazet@...gle.com>

Applied, thanks Eric.
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