From mboxrd@z Thu Jan 1 00:00:00 1970 From: James Carlson Subject: Re: [PATCH, untested] Support for PPPOE on SMP Date: Thu, 26 Jun 2003 06:51:30 -0400 (EDT) Sender: netdev-bounce@oss.sgi.com Message-ID: <16122.53298.150512.793074@h006008986325.ne.client2.attbi.com> References: <20030625.143334.85380461.davem@redhat.com> <20030626035824.D68B62C147@lists.samba.org> <20030625.205941.41631020.davem@redhat.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Transfer-Encoding: 7bit Cc: rusty@rustcorp.com.au, paulus@samba.org, netdev@oss.sgi.com, fcusack@samba.org Return-path: To: "David S. Miller" In-Reply-To: David S. Miller's message of 25 June 2003 20:59:41 Errors-to: netdev-bounce@oss.sgi.com List-Id: netdev.vger.kernel.org David S. Miller writes: > From: Rusty Russell > Date: Thu, 26 Jun 2003 13:57:09 +1000 > > Frankly, I'm amazed anyone sees reordering in real life... > > Many paths on the internet are quite reordered, this is > the first thing. In fact, I claim that any TCP stack that > doesn't do reordering detection is busted performance wise. Nobody's disputing that. That's certainly true. However, reordering on a given wire does not happen. > The second thing is that network cards can and do reorder packets. > Some PCMCIA cards do this just for fun. If so, then that needs to be taken up with the manufacturer. That's a rather severe design flaw that will prevent such a card from ever being used for anything other than IP -- many other protocols *ASSUME* that packets on a single wire cannot be reordered, including SNA, PPP (!), and link aggregation, among others. > And ethernet _DOES NOT_ > guarentee non-reordering. Please provide references. 802.1 MAC says otherwise. > At a minumum, a card can use QoS values to > reorder receive of a given packet, it can also use this to reorder > transmit. Our packet schedulers do this on a software level. Sure. *If* QoS is present, then reordering between priority levels is permissible. However, reordering L2 frames at a given priority level isn't. > If you need ordering, you need sequence numbers in your > protocol if you wish to operate over these mediums. > > The case where SMP causes out-of-order packet delivery is just > academic compared to the non-local sources of reordering > mentioned above. Not where it affects the correctness of the defined protocols. -- James Carlson