netdev - Re: [RFC net-next] net: track locally triggered link loss

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Date:   Sat, 21 May 2022 16:23:16 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, linux@...linux.org.uk, olteanv@...il.com,
        hkallweit1@...il.com, f.fainelli@...il.com, saeedm@...dia.com,
        michael.chan@...adcom.com
Subject: Re: [RFC net-next] net: track locally triggered link loss

> For a system which wants to monitor link quality on the local end =>
> i.e. whether physical hardware has to be replaced - differentiating
> between (1) and (2) doesn't really matter, they are both non-events.

Maybe data centres should learn something from the automotive world.
It seems like most T1 PHYs have a signal quality value, which is
exposed via netlink in the link info message. And it is none invasive.

Many PHYs also have counters of receive errors, framing errors
etc. These can be reported via ethtool --phy-stats.

SFPs expose SNR ratios in their module data, transmit and receive
powers etc, via ethtool -m and hwmon.

There is also ethtool --cable-test. It is invasive, in that it
requires the link to go down, but it should tell you about broken
pairs. However, you probably know that already, a monitoring system
which has not noticed the link dropping to 100Mbps so it only uses two
pairs is not worth the money you paired for it.

Now, it seems like very few, if any, firmware driven Ethernet card
actually make use of these features. You need cards which Linux is
actually driving the hardware. But these APIs are available for
anybody to use. Don't data centre users have enough purchasing power
they can influence firmware/driver writers to actually use these APIs?
And i think the results would be better than trying to count link
up/down.

     Andrew