From mboxrd@z Thu Jan  1 00:00:00 1970
From: David Miller <davem@davemloft.net>
Subject: Re: [PATCH net-next] tcp: introduce TCPSpuriousRtxHostQueues SNMP
 counter
Date: Thu, 18 Apr 2013 14:57:45 -0400 (EDT)
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From: Eric Dumazet <eric.dumazet@gmail.com>
Date: Thu, 18 Apr 2013 09:52:51 -0700

> From: Eric Dumazet <edumazet@google.com>
> 
> Host queues (Qdisc + NIC) can hold packets so long that TCP can
> eventually retransmit a packet before the first transmit even left
> the host.
> 
> Its not clear right now if we could avoid this in the first place :
> 
> - We could arm RTO timer not at the time we enqueue packets, but
>   at the time we TX complete them (tcp_wfree())
> 
> - Cancel the sending of the new copy of the packet if prior one
>   is still in queue.
> 
> This patch adds instrumentation so that we can at least see how
> often this problem happens.
> 
> TCPSpuriousRtxHostQueues SNMP counter is incremented every time
> we detect the fast clone is not yet freed in tcp_transmit_skb()
> 
> Signed-off-by: Eric Dumazet <edumazet@google.com>

Applied, thanks.