netdev - Re: TCP and reordering

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Message-ID: <1354107140.14302.140.camel@edumazet-glaptop>
Date:	Wed, 28 Nov 2012 04:52:20 -0800
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	David Woodhouse <dwmw2@...radead.org>
Cc:	Vijay Subramanian <subramanian.vijay@...il.com>,
	David Miller <davem@...emloft.net>, saku@...i.fi,
	rick.jones2@...com, netdev@...r.kernel.org
Subject: Re: TCP and reordering

On Wed, 2012-11-28 at 12:39 +0000, David Woodhouse wrote:

> 
> I'll go back to looking at TSQ, and BQL for PPP. If I have to use
> skb_orphan() and install a destructor of my own in order to do BQL for
> PPP, that'll upset TSQ a little. Is there a way we could *chain* the
> destructors... skb_clone() to put the skbs on the PPP channels' queues,
> perhaps, then free the original from the PPP destructor? Or is that too
> much overhead?
> 
> I've killed most of the channel queue for PPPoATM and PPPoE now, but
> L2TP still has a whole load of buffering all the way through the stack
> again before it really leaves the host.
> 
> (And PPPoE will still have the txqueuelen on the Ethernet device too).
> 

BQL is nice for high speed adapters.

For slow one, you always can stop the queue for each packet given to
start_xmit()

And restart the queue at TX completion.

Some device drivers do that (because the hardware has a single slot, no
ring buffer, not because they wanted to fight bufferbloat ;) )



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