netdev - Re: [PATCH net-next v2 2/8] docs: net: include the new ethtool pause stats in the stats doc

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Message-ID: <961c3983df3e42b5cd6da909c69a0fa1f5c5c850.camel@nvidia.com>
Date:   Mon, 14 Sep 2020 21:19:25 +0000
From:   Saeed Mahameed <saeedm@...dia.com>
To:     "kuba@...nel.org" <kuba@...nel.org>
CC:     "mkubecek@...e.cz" <mkubecek@...e.cz>,
        Tariq Toukan <tariqt@...dia.com>,
        "michael.chan@...adcom.com" <michael.chan@...adcom.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "alexander.duyck@...il.com" <alexander.duyck@...il.com>,
        "andrew@...n.ch" <andrew@...n.ch>
Subject: Re: [PATCH net-next v2 2/8] docs: net: include the new ethtool pause
 stats in the stats doc

On Mon, 2020-09-14 at 12:52 -0700, Jakub Kicinski wrote:
> On Mon, 14 Sep 2020 19:33:08 +0000 Saeed Mahameed wrote:
> > > +Protocol-specific statistics
> > > +----------------------------
> > > +
> > > +Some of the interfaces used for configuring devices are also
> > > able
> > > +to report related statistics. For example ethtool interface used
> > > +to configure pause frames can report corresponding hardware
> > > counters::
> > > +
> > > +  $ ethtool --include-statistics -a eth0
> > > +  Pause parameters for eth0:
> > > +  Autonegotiate:	on
> > > +  RX:			on
> > > +  TX:			on
> > > +  Statistics:
> > > +    tx_pause_frames: 1
> > > +    rx_pause_frames: 1
> > > +  
> > 
> > this will require to access the HW twice per stats request to read
> > both
> > stats and current parameters, maybe this is not a big deal, but
> > sharp
> > accuracy can be important for some performance enthusiasts.
> > 
> > Do we need an API that only reports statistics without the current
> > parameters ?
> 
> That crossed my mind. IDK how real this concern is if we have ethtool
> -S which dumps half of the universe and nobody ever done anything
> about it..
> 
> Once we start adding more interfaces (as I said elsewhere I plan to
> add
> FEC counters) we'll also have to do multiple calls for multiple types
> of stats. But I think that's fine as a starting point. We can extend
> RTM_GETSTATS to provide an efficient interface when needed.
> 
> As you may recall a couple years back I posted a set with
> "hierarchical
> stats" which as an attempt to solve all the problems at once. 
> I concluded that it's a wrong approach. We should start with the
> simple
> and obvious stuff. We can build complexity later.

Agreed.