netdev - Re: txqueuelen has wrong units; should be time

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Message-ID: <1299084644.2920.24.camel@edumazet-laptop>
Date:	Wed, 02 Mar 2011 17:50:44 +0100
From:	Eric Dumazet <eric.dumazet@...il.com>
To:	Mikael Abrahamsson <swmike@....pp.se>
Cc:	Stephen Hemminger <shemminger@...tta.com>,
	John Heffner <johnwheffner@...il.com>,
	Bill Sommerfeld <wsommerfeld@...gle.com>,
	Hagen Paul Pfeifer <hagen@...u.net>,
	Albert Cahalan <acahalan@...il.com>,
	Jussi Kivilinna <jussi.kivilinna@...et.fi>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	netdev@...r.kernel.org
Subject: Re: txqueuelen has wrong units; should be time

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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