Re: [PATCH, untested] Support for PPPOE on SMP

David S. Miller writes:

   From: Rusty Russell [off-list ref]
   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                                  [off-list ref]

On Thu, 26 Jun 2003, James Carlson wrote:

David S. Miller writes:
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.

So what about packet being loss? Wouldnt that ensure reordering?
And there is no such thing as a lossless wire.

cheers,
jamal

PS:- Paulus i wasnt preaching getting rid of ppp/pppoe although its
a nice thouhgt. More fix linux pppd and pppoe ;->