Flow ID, LACP, and igb

[Barney Cordoba]

Comcast sends packets OOO. With any decent number of internet hops you're likely to encounter a load
balancer or packet shaper that sends packets OOO, so you just can't be worried about it. In fact, your
designs MUST work with OOO packets. 

Getting balance on your load balanced lines is certainly a bigger upside than the additional CPU used.
You can buy a faster processor for your "stack" for a lot less than you can buy bandwidth. 

Frankly my opinion of LRO is that it's a science project suitable for labs only. It's a trick to get more bandwidth
than your bus capacity; the answer is to not run PCIe2 if you need pcie3. You can use it internally if you have
control of all of the machines. When I modify a driver the first thing that I do is rip it out.

BC


________________________________
 From: Luigi Rizzo <rizzo at iet.unipi.it>
To: Barney Cordoba <barney_cordoba at yahoo.com> 
Cc: Andre Oppermann <andre at freebsd.org>; Alan Somers <asomers at freebsd.org>; "net at freebsd.org" <net at freebsd.org>; Jack F Vogel <jfv at freebsd.org>; Justin T. Gibbs <gibbs at freebsd.org>; T.C. Gubatayao <tgubatayao at barracuda.com> 
Sent: Saturday, August 31, 2013 10:27 PM
Subject: Re: Flow ID, LACP, and igb
 

On Sun, Sep 1, 2013 at 4:15 AM, Barney Cordoba <barney_cordoba at yahoo.com>wrote:

> ...
>

[your point on testing with realistic assumptions is surely a valid one]


>
> Of course there's nothing really wrong with OOO packets. We had this
> discussion before; lots of people
> have round robin dual homing without any ill effects. It's just not an
> issue.
>

It depends on where you are.
It may not be an issue if the reordering is not large enough to
trigger retransmissions, but even then it is annoying as it causes
more work in the endpoint -- it prevents LRO from working, and even
on the host stack it takes more work to sort where an out of order
segment goes than appending an in-order one to the socket buffer.

cheers
luigi
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