Re: TCP and reordering

[Eric Dumazet <eric.dumazet@gmail.com>]

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 ;) )