netdev - Re: [PATCH] net: ethernet: ti: cpsw_ale: optimize cpsw_ale

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Message-ID: <20221111120350.waumn6x35vwfnrfc@skbuf>
Date:   Fri, 11 Nov 2022 12:03:54 +0000
From:   Vladimir Oltean <vladimir.oltean@....com>
To:     Jakub Kicinski <kuba@...nel.org>
CC:     Roger Quadros <rogerq@...nel.org>,
        Ido Schimmel <idosch@...sch.org>,
        Nikolay Aleksandrov <razor@...ckwall.org>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "edumazet@...gle.com" <edumazet@...gle.com>,
        "pabeni@...hat.com" <pabeni@...hat.com>,
        "vigneshr@...com" <vigneshr@...com>, "srk@...com" <srk@...com>,
        "linux-omap@...r.kernel.org" <linux-omap@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: ethernet: ti: cpsw_ale: optimize cpsw_ale_restore()

On Thu, Nov 10, 2022 at 12:32:49PM -0800, Jakub Kicinski wrote:
> > I have a question here. How should ageable entries be treated in this case?
> 
> Ah, no idea :) Let's me add experts to To:

Not a real expert, but if suspend/resume loses the Ethernet link,
I expect that no dynamically learned entries are preserved across
a link loss event.

In DSA for example, we only keep ageable entries in hardware as long as
the port STP state, plus BR_LEARNING port flag, are compatible with
having such FDB entries. Otherwise, any transition to such a state
flushes the ageable FDB entries.

A link loss generates a bridge port transition to the DISABLED state,
which DSA uses to generate a SWITCHDEV_FDB_FLUSH_TO_BRIDGE event.

I'm not sure if it would even be possible to accurately do the right
thing and update the ageing timer of the FDB entries with the amount of
time that the system was suspended.