netdev - Re: [PATCH net-next v1 1/1] net: dsa: microchip: add stats64 support for ksz8 series of switches

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Message-ID: <20221207154826.5477008b@kernel.org>
Date:   Wed, 7 Dec 2022 15:48:26 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Oleksij Rempel <o.rempel@...gutronix.de>
Cc:     Woojung Huh <woojung.huh@...rochip.com>,
        Andrew Lunn <andrew@...n.ch>, Arun.Ramadoss@...rochip.com,
        Florian Fainelli <f.fainelli@...il.com>,
        "David S. Miller" <davem@...emloft.net>, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, UNGLinuxDriver@...rochip.com,
        Eric Dumazet <edumazet@...gle.com>, kernel@...gutronix.de,
        Paolo Abeni <pabeni@...hat.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Vivien Didelot <vivien.didelot@...il.com>
Subject: Re: [PATCH net-next v1 1/1] net: dsa: microchip: add stats64
 support for ksz8 series of switches

On Wed, 7 Dec 2022 07:16:30 +0100 Oleksij Rempel wrote:
> > FWIW for normal netdevs / NICs the rtnl_link_stat pkts do not include
> > pause frames, normally. Otherwise one can't maintain those stats in SW
> > (and per-ring stats, if any, don't add up to the full link stats).
> > But if you have a good reason to do this - I won't nack..  
> 
> Pause frames are accounted by rx/tx_bytes by HW. Since pause frames may
> have different size, it is not possible to correct byte counters, so I
> need to add them to the packet counters.

I have embarrassed myself with my lack of understanding of pause frames
before but nonetheless - are you sure?  I thought they are always 64B.
Quick look at the standard seems to agree:

 31C.3.1 Receive state diagram (INITIATE MAC CONTROL FUNCTION) for
         EXTENSION operation

shows a 64 octet frame.

Sending long pause frames seems self-defeating as we presumably want
the receiver to react ASAP.