netdev - Re: [PATCH net-next v2 0/8] ethtool: add pause frame stats

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Message-ID: <20200914085306.5e00833b@kicinski-fedora-pc1c0hjn.dhcp.thefacebook.com>
Date:   Mon, 14 Sep 2020 08:53:06 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Vladimir Oltean <olteanv@...il.com>, davem@...emloft.net,
        netdev@...r.kernel.org, mkubecek@...e.cz,
        michael.chan@...adcom.com, tariqt@...dia.com, saeedm@...dia.com,
        alexander.duyck@...il.com, andrew@...n.ch
Subject: Re: [PATCH net-next v2 0/8] ethtool: add pause frame stats

On Fri, 11 Sep 2020 19:54:11 -0700 Florian Fainelli wrote:
> > I think I'm missing the problem you're trying to describe.
> > Are you making a general comment / argument on ethtool stats?
> > 
> > Pause stats are symmetrical - as can be seen in your quote
> > what's RX for the CPU is TX for the switch, and vice versa.
> > 
> > Since ethtool -A $cpu_mac controls whether CPU netdev generates
> > and accepts pause frames, correspondingly the direction and meaning
> > of pause statistics on that interface is well defined.
> > 
> > You can still append your custom CPU port stats to ethtool -S or
> > debugfs or whatnot, but those are only useful for validating that
> > the configuration of the CPU port is not completely broken. Otherwise
> > the counters are symmetrical. A day-to-day user of the device doesn't
> > need to see both of them.  
> 
> It would be a lot easier to append the stats if there was not an 
> additional ndo introduce to fetch the pause statistics because DSA 
> overlay ndo on a function by function basis. Alternatively we should 
> consider ethtool netlink operations over a devlink port at some point so 
> we can get rid of the ugly ndo and ethtool_ops overlay that DSA does.

I'm trying to target the 99.9% of users here, so in all honesty I'm
concerned that if we try to cater to strange corner cases too much 
the entire interface will suffer. Hence I decided not to go with
devlink, but extend the API people already know and use. It's the most
logical and obvious place to me.

> Can we consider using get_ethtool_stats and ETH_SS_PAUSE_STATS as a 
> stringset identifier? That way there is a single point within driver to 
> fetch stats.

Can you say more? There are no strings reported in this patch set.