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Message-ID: <3D690D10.5040601@candelatech.com>
Date: Sun, 25 Aug 2002 10:00:00 -0700
From: Ben Greear <greearb@candelatech.com>
Organization: Candela Technologies
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To: Alan Cox <alan@lxorguk.ukuu.org.uk>
CC: linux-kernel <linux-kernel@vger.kernel.org>
Subject: Re: packet re-ordering on SMP machines.
References: <3D6884BC.5090004@candelatech.com> <1030286473.16651.7.camel@irongate.swansea.linux.org.uk>
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Alan Cox wrote:
> On Sun, 2002-08-25 at 08:18, Ben Greear wrote:
> 
>>By re-ordered, I mean that a method called from process_backlog in dev.c
>>is being handed packets in a different order than they are being poked into
>>the driver with hard_start_xmit on the other interface.  If each CPU can be running the
>>process_backlog, then I can see how this could be happening.
>>
>>
>>1)  Is this expected behaviour?
> 
> Yes
> 
> 
>>2)  Is there any standard (ie configurable) way to enforce strict ordering on an
>>     SMP system?
> 
> No
> 
> 
>>3)  If answer to 2 is no, would you all be interested in a patch that
>>     did allow strict ordering (if indeed I can figure out how to write one)?
> 
> 
> You should never need it. Ethernet, hubs, switches, routers, internet
> backbones etc will all cause packet re-ordering. You should also expect
> the percentage of re-ordered frames on the net to rise and rise. 

I would like to detect the number of pkts that such backbone hardware does
re-order, so if my end machine is also re-ordering, I cannot get valid
numbers.

Thanks,
Ben

> 
> 
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-- 
Ben Greear <greearb@candelatech.com>       <Ben_Greear AT excite.com>
President of Candela Technologies Inc      http://www.candelatech.com
ScryMUD:  http://scry.wanfear.com     http://scry.wanfear.com/~greear


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