netdev - Re: [PATCH net-next v1 2/3] net: dsa: ar9331: add support for pause stats

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Date:   Tue, 28 Jun 2022 10:45:04 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Andrew Lunn <andrew@...n.ch>
Cc:     Jakub Kicinski <kuba@...nel.org>,
        Woojung Huh <woojung.huh@...rochip.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        "David S. Miller" <davem@...emloft.net>,
        Eric Dumazet <edumazet@...gle.com>,
        Lukas Wunner <lukas@...ner.de>, kernel@...gutronix.de,
        Paolo Abeni <pabeni@...hat.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>,
        UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next v1 2/3] net: dsa: ar9331: add support for pause
 stats

On Tue, Jun 28, 2022 at 09:22:53AM +0200, Andrew Lunn wrote:
> > Yeah, the corrections are always iffy. I understand the doubts, and we
> > can probably leave things "under-specified" until someone with a strong
> > preference comes along. But I hope that the virt example makes it clear
> > that neither of the choices is better (SR-IOV NICs would have to start
> > adding the pause if we declare rtnl stats as inclusive).
> > 
> > I can see advantages to both counting (they are packets) and not
> > counting those frames (Linux doesn't see them, they get "invented" 
> > by HW).
> > 
> > Stats are hard.
> 
> I doubt we can define it either way. I once submitted a patch for one
> driver to make it ignore CRC bytes. It then gave the exact same counts
> as another hardware i was using, making the testing i was doing
> simpler.
> 
> The patch got rejected simply because we have both, with CRC and
> without CRC, neither is correct, neither is wrong.
> 
> So i would keep it KISS, pause frames can be included, but i would not
> go to extra effort to include them, or to exclude them.

After I started investigating this topic, I was really frustrated. It is
has hard to find what is wrong: my patch is not working and flow
controller is not triggered? Or every HW/driver implements counters in
some own way. Same is about byte counts: for same packet with different
NICs i have at least 3 different results: 50, 64 and 68.
It makes testing and validation a nightmare. 

Regards,
Oleksij
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