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

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Message-ID: <b3f766f9-498a-a529-0e37-c6afa440dbd5@gmail.com>
Date:   Mon, 14 Sep 2020 09:25:44 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Jakub Kicinski <kuba@...nel.org>
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 9/14/2020 8:53 AM, Jakub Kicinski wrote:
> 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.

What I am suggesting is that we have a central and unique method for 
drivers to be called for all ethtool statisitcs to be obtained, and not 
create another ethtool operation specifically for pause stats.

Today we have get_ethtool_stats and a stringset argument that tells you 
which type of statistic to return. I am not suggesting that we return 
strings or that it should be necessary for fetching pause stats.
-- 
Florian