netdev - Re: AW: AW: RFC: replace packets already in queue

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Message-ID: <1341266168.22621.466.camel@edumazet-glaptop>
Date:	Mon, 02 Jul 2012 23:56:08 +0200
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Nicolas de Pesloüan 
	<nicolas.2p.debian@...il.com>
Cc:	"Erdt, Ralph" <ralph.erdt@...e.fraunhofer.de>,
	Rick Jones <rick.jones2@...com>,
	"netdev@...r.kernel.org" <netdev@...r.kernel.org>
Subject: Re: AW: AW: RFC: replace packets already in queue

On Mon, 2012-07-02 at 22:32 +0200, Nicolas de Pesloüan wrote:
> Le 02/07/2012 10:38, Erdt, Ralph a écrit :
> >>> Even if the wireless queue is a problem (because of our setup, this
> >> is
> >>> not a problem), the network stack queue (*) is the biggest queue, and
> >>> a good point to optimize.
> >>
> >> Hmm, I am not convinced you have no queues on wireless.
> >>
> >> Please describe how you managed this.
> >>
> >> In fact this is the biggest problem with wireless : mac82011 framework
> >> aggressively pull packets from Linux packet qdisc in order to perform
> >> packet aggregation.
> >
> > I did not talking about W-LAN (802.11). I'm talking about an property technology which is able to
> > send over KILOMETERs (WLAN<  100m) but with VERY low bandwidth: 9600 bit (no Mega, Giga or Kilo!)
> > (W-LAN: slowest: 1Mbit). The devices is loosely connected to our boxes: No linux driver but a
> > program which create an virtual network device. This just sends one packet to the devices and
> > then waits for the acknowledgement that the packet was sent. THEN the next packet will be send.
> > There is no further queue, because the wireless is so lame, that there is no need for that! (BTW:
> > the qdisc and the connector are distinct problems/programs. There is no dependency.)
> 
> If I were you, I would use a tun/tap interface and manage a private packet queue in userspace. This 
> way, you wouldn't have to manage the overhead of porting your kernel code to every new kernel versions.
> 

This seems a good idea.

Then you can do other coalescing stuff, like TCP ACK that could be
aggregated to single ACK as well.



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