netdev - Re: [PATCH net-next] fq_codel: report congestion notification at enqueue time

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Date:	Fri, 29 Jun 2012 06:50:57 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Dave Taht <dave.taht@...il.com>
Cc:	Yuchung Cheng <ycheng@...gle.com>,
	David Miller <davem@...emloft.net>,
	netdev <netdev@...r.kernel.org>, codel@...ts.bufferbloat.net,
	Tom Herbert <therbert@...gle.com>,
	Matt Mathis <mattmathis@...gle.com>,
	Nandita Dukkipati <nanditad@...gle.com>,
	Neal Cardwell <ncardwell@...gle.com>,
	Andrew McGregor <andrewmcgr@...il.com>
Subject: Re: [PATCH net-next] fq_codel: report congestion notification at
 enqueue time

On Thu, 2012-06-28 at 19:47 -0400, Dave Taht wrote: 
> On Thu, Jun 28, 2012 at 6:56 PM, Yuchung Cheng <ycheng@...gle.com> wrote:
> > On Thu, Jun 28, 2012 at 11:12 AM, Eric Dumazet <eric.dumazet@...il.com> wrote:
> >> On Thu, 2012-06-28 at 10:51 -0700, Dave Taht wrote:
> >>
> >>> clever idea. A problem is there are other forms of network traffic on
> >>> a link, and this is punishing a single tcp
> > Dave: it won't just punish a single TCP, all protocols that react to
> > XMIT_CN will share similar fate.
> 
> What protocols in the kernel do and don't? was the crux of this question.
> 

AFAIK that only tcp cares a bit, or seems to.

But not that much, since it continues to send packets.

Thats because tcp_transmit_skb() changes the NET_XMIT_CN status to plain
NET_XMIT_SUCCESS.

My long term plan is to reduce number of skbs queued in Qdisc for TCP
stack, to reduce RTT (removing the artificial RTT bias because of local
queues)

> I'm not objecting to the idea, it's clever, as I said. I'm thinking I'll
> apply it to cerowrt's next build and see what happens, if this
> will apply against 3.3. Or maybe the ns3 model. Or both.

A router will have no use of this feature, not sure you need to spend
time trying this ;)



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