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From: Vladimir Oltean <vladimir.oltean@nxp.com>
To: Heiner Kallweit <hkallweit1@gmail.com>
Cc: "netdev@vger.kernel.org" <netdev@vger.kernel.org>,
	"andrew@lunn.ch" <andrew@lunn.ch>,
	"f.fainelli@gmail.com" <f.fainelli@gmail.com>,
	"vivien.didelot@gmail.com" <vivien.didelot@gmail.com>,
	"kuba@kernel.org" <kuba@kernel.org>,
	Christian Eggers <ceggers@arri.de>,
	Kurt Kanzenbach <kurt@linutronix.de>
Subject: Re: [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics
Date: Sun, 18 Oct 2020 13:48:44 +0000
Message-ID: <20201018134843.emustnvgyby32cm4@skbuf> (raw)
In-Reply-To: <19f10bf4-4154-2207-6554-e44ba05eed8a@gmail.com>

On Sun, Oct 18, 2020 at 03:09:32PM +0200, Heiner Kallweit wrote:
> 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.

2^32 = 4,294,967,296 = 4 billion packets
Considering that every packet that needs TX timestamping must be
reallocated, protocols such as IEEE 802.1AS will trigger 5 reallocs per
second. So time synchronization alone (background traffic, by all
accounts) will make this counter overflow in 27 years.
Every packet flooded or multicast by the bridge will also trigger
reallocs. In this case it is not difficult to imagine that overflows
might occur sooner.

Even if the above wasn't true. What becomes easier when I make the
counter an unsigned long? I need to make arch-dependent casts between an
unsigned long an an u64 when I expose the counter to ethtool, and there
it ends up being u64 too, doesn't it?

  reply index

Thread overview: 49+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-10-17 21:35 [RFC PATCH 00/13] Generic TX reallocation for DSA Vladimir Oltean
2020-10-17 21:35 ` [RFC PATCH 01/13] net: dsa: add plumbing for custom netdev statistics Vladimir Oltean
2020-10-17 22:13   ` Florian Fainelli
2020-10-17 23:15   ` Andrew Lunn
2020-10-18  0:23     ` Vladimir Oltean
2020-10-18 12:02   ` Heiner Kallweit
2020-10-18 12:16     ` Vladimir Oltean
2020-10-18 13:09       ` Heiner Kallweit
2020-10-18 13:48         ` Vladimir Oltean [this message]
2020-10-18 14:13           ` Heiner Kallweit
2020-10-18 22:58             ` Vladimir Oltean
2020-10-18 23:11               ` Florian Fainelli
2020-10-19  0:21                 ` Vladimir Oltean
2020-10-19  3:49                   ` Florian Fainelli
2020-10-19 12:05                     ` Andrew Lunn
2020-10-19 16:27                       ` Florian Fainelli
2020-10-18 16:49   ` Jakub Kicinski
2020-10-18 17:36     ` Andrew Lunn
2020-10-18 18:26       ` Jakub Kicinski
2020-10-18 18:33         ` Jakub Kicinski
2020-10-17 21:36 ` [RFC PATCH 02/13] net: dsa: implement a central TX reallocation procedure Vladimir Oltean
2020-10-17 22:01   ` Vladimir Oltean
2020-10-17 22:11     ` Florian Fainelli
2020-10-17 22:17       ` Vladimir Oltean
2020-10-18  0:37         ` Florian Fainelli
2020-10-19  8:33       ` David Laight
2020-10-19 10:30         ` Vladimir Oltean
2020-10-19 11:14           ` David Laight
2020-10-19 11:41             ` Vladimir Oltean
2020-10-19 12:19           ` Andrew Lunn
2020-10-17 22:31     ` Vladimir Oltean
2020-10-18  0:13       ` Vladimir Oltean
2020-10-18 10:36         ` Christian Eggers
2020-10-18 11:42           ` Vladimir Oltean
2020-10-18 11:59             ` Christian Eggers
2020-10-18 12:15               ` Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 03/13] net: dsa: tag_ksz: don't allocate additional memory for padding/tagging Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 04/13] net: dsa: trailer: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 05/13] net: dsa: tag_qca: let DSA core deal with TX reallocation Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 06/13] net: dsa: tag_ocelot: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 07/13] net: dsa: tag_mtk: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 08/13] net: dsa: tag_lan9303: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 09/13] net: dsa: tag_edsa: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 10/13] net: dsa: tag_brcm: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 11/13] net: dsa: tag_dsa: " Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 12/13] net: dsa: tag_gswip: " Vladimir Oltean
2020-10-17 22:19   ` Vladimir Oltean
2020-10-17 21:36 ` [RFC PATCH 13/13] net: dsa: tag_ar9331: " Vladimir Oltean
2020-10-17 23:07 ` [RFC PATCH 00/13] Generic TX reallocation for DSA Andrew Lunn

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