netdev - Re: [PATCH next] bonding: Extending LACP MUX State Machine to include a Collecting State.

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Date: Thu, 21 Dec 2023 21:38:01 -0800
From: David Dillow <dave@...dillows.org>
To: jay.vosburgh@...onical.com
Cc: aahila@...gle.com, andy@...yhouse.net, daniel@...earbox.net,
        davem@...emloft.net, edumazet@...gle.com, herbert@...dor.apana.org.au,
        kuba@...nel.org, linux-kernel@...r.kernel.org, maheshb@...gle.com,
        martin.lau@...nel.org, netdev@...r.kernel.org, pabeni@...hat.com
Subject: Re: [PATCH next] bonding: Extending LACP MUX State Machine to
 include a Collecting State.

> I haven't read the patch in detail yet, but my overall question
> is: why do we need this?  This adds significant complexity to the
> state machine logic.  What real problem is this solving, i.e., what
> examples do you have of systems where a port is "in a state where
> it can receive incoming packets while not still distributing"?

Any time we add a new link to an aggregator, or the bond selects a new
aggegrator based on the selection policy, there is currently a race
where we start distributing traffic before our partner (usually a
switch) is ready to start collecting it, leading to dropped packets if
we're running traffic over the bond. We reliably hit this window,
making what should be a non-issue into a customer-visible packet-loss
event. Implementing the full state machine closes the window and makes
these maintenance events lossless.