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Subject: Re: txqueuelen has wrong units; should be time
From: Eric Dumazet <eric.dumazet@gmail.com>
To: Mikael Abrahamsson <swmike@swm.pp.se>
Cc: Stephen Hemminger <shemminger@vyatta.com>,
        John Heffner <johnwheffner@gmail.com>,
        Bill Sommerfeld <wsommerfeld@google.com>,
        Hagen Paul Pfeifer <hagen@jauu.net>,
        Albert Cahalan <acahalan@gmail.com>,
        Jussi Kivilinna <jussi.kivilinna@mbnet.fi>,
        linux-kernel <linux-kernel@vger.kernel.org>, netdev@vger.kernel.org
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Date: Wed, 02 Mar 2011 17:50:44 +0100
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Le mercredi 02 mars 2011 à 17:41 +0100, Mikael Abrahamsson a écrit :
> On Tue, 1 Mar 2011, Stephen Hemminger wrote:
> 
> > Also WRED is not default on faster links because it can't be done fast 
> > enough.
> 
> Before this propagates as some kind of truth. Cisco modern core routers 
> have no problems doing WRED at wirespeed, the above statement is not true.
> 

looking at cisco docs you provided
( <http://www.cisco.com/en/US/docs/ios/12_0s/feature/guide/12stbwr.html>
 )
, it seems the WRED time limits (instead of bytes/packets limits) are
internaly converted to bytes/packets limits


quote : 

When the queue limit threshold is specified in milliseconds, the number
of milliseconds is internally converted to bytes using the bandwidth
available for the class. 


So it seems its only a facility provided, and queues are still managed
with bytes/packets limits...

WRED is able to prob drop a packet when this packet is enqueued. At time
of enqueue, we dont know yet the time of dequeue, unless bandwidth is
known.


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