netdev - Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics

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Date:   Sun, 18 Oct 2020 15:09:32 +0200
From:   Heiner Kallweit <hkallweit1@...il.com>
To:     Vladimir Oltean <vladimir.oltean@....com>
Cc:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "andrew@...n.ch" <andrew@...n.ch>,
        "f.fainelli@...il.com" <f.fainelli@...il.com>,
        "vivien.didelot@...il.com" <vivien.didelot@...il.com>,
        "kuba@...nel.org" <kuba@...nel.org>,
        Christian Eggers <ceggers@...i.de>,
        Kurt Kanzenbach <kurt@...utronix.de>
Subject: Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev
 statistics

On 18.10.2020 14:16, Vladimir Oltean wrote:
> On Sun, Oct 18, 2020 at 02:02:46PM +0200, Heiner Kallweit wrote:
>> Wouldn't a simple unsigned long (like in struct net_device_stats) be
>> sufficient here? This would make handling the counter much simpler.
>> And as far as I understand we talk about a packet counter that is
>> touched in certain scenarios only.
> 
> I don't understand, in what sense 'sufficient'? This counter is exported
> to ethtool which works with u64 values, how would an unsigned long,
> which is u32 on 32-bit systems, help?
> 
Sufficient for me means that it's unlikely that a 32 bit counter will
overflow. Many drivers use the 32 bit counters (on a 32bit system) in
net_device_stats for infrequent events like rx/tx errors, and 64bit
counters only for things like rx/tx bytes, which are more likely to
overflow.