netdev - Re: [PATCH net-next] ethtool: linkstate: add a statistic for PHY down events

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Date:   Wed, 26 Oct 2022 14:19:08 +0200
From:   Andrew Lunn <andrew@...n.ch>
To:     Jakub Kicinski <kuba@...nel.org>
Cc:     davem@...emloft.net, netdev@...r.kernel.org, edumazet@...gle.com,
        pabeni@...hat.com, saeedm@...dia.com, corbet@....net,
        michael.chan@...adcom.com, huangguangbin2@...wei.com,
        chenhao288@...ilicon.com, moshet@...dia.com,
        linux@...pel-privat.de, linux-doc@...r.kernel.org
Subject: Re: [PATCH net-next] ethtool: linkstate: add a statistic for PHY
 down events

On Tue, Oct 25, 2022 at 07:09:48PM -0700, Jakub Kicinski wrote:
> The previous attempt to augment carrier_down (see Link)
> was not met with much enthusiasm so let's do the simple
> thing of exposing what some devices already maintain.
> Add a common ethtool statistic for link going down.
> Currently users have to maintain per-driver mapping
> to extract the right stat from the vendor-specific ethtool -S
> stats. carrier_down does not fit the bill because it counts
> a lot of software related false positives.
> 
> Add the statistic to the extended link state API to steer
> vendors towards implementing all of it.
> 
> Implement for bnxt. mlx5 and (possibly) enic also have
> a counter for this but I leave the implementation to their
> maintainers.

> +struct ethtool_link_ext_stats {
> +	/* Custom Linux statistic for PHY level link down events.
> +	 * In a simpler world it should be equal to netdev->carrier_down_count
> +	 * unfortunately netdev also counts local reconfigurations which don't
> +	 * actually take the physical link down, not to mention NC-SI which,
> +	 * if present, keeps the link up regardless of host state.
> +	 * This statistic counts when PHY _actually_ went down, or lost link.
> +	 */
> +	u64 LinkDownEvents;
> +};

You might want to consider a generic implementation in phylib. You
should then have over 60 drivers implementing this, enough momentum it
might actually get used.

      Andrew