netdev - Re: [PATCH net-next] tcp: introduce TCPSpuriousRtxHostQueues SNMP counter

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Message-ID: <1366308381.3205.66.camel@edumazet-glaptop>
Date:	Thu, 18 Apr 2013 11:06:21 -0700
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Stephen Hemminger <stephen@...workplumber.org>
Cc:	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>,
	Yuchung Cheng <ycheng@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Tom Herbert <therbert@...gle.com>,
	Willem de Bruijn <willemb@...gle.com>
Subject: Re: [PATCH net-next] tcp: introduce TCPSpuriousRtxHostQueues SNMP
 counter

On Thu, 2013-04-18 at 10:45 -0700, Stephen Hemminger wrote:
> On Thu, 18 Apr 2013 09:52:51 -0700
> Eric Dumazet <eric.dumazet@...il.com> wrote:
> 
> > From: Eric Dumazet <edumazet@...gle.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.
> 
> I though you were use fq_codel ;-) and that wouldn't happen.

Remind that fq_codel drops packets at dequeue time only ;)

So TCP stack could retransmit while prior packet is still in fq_codel
queue.



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