netdev - RE: [PATCH net-next 1/3] net: ethtool: add support for forward error correction modes

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Date:   Thu, 6 Jul 2017 21:06:09 +0000
From:   "Wyborny, Carolyn" <carolyn.wyborny@...el.com>
To:     Jakub Kicinski <kubakici@...pl>, Casey Leedom <leedom@...lsio.com>
CC:     Dustin Byford <dustin@...ulusnetworks.com>,
        Andrew Lunn <andrew@...n.ch>,
        Roopa Prabhu <roopa@...ulusnetworks.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "linville@...driver.com" <linville@...driver.com>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "vidya.chowdary@...il.com" <vidya.chowdary@...il.com>,
        "olson@...ulusnetworks.com" <olson@...ulusnetworks.com>,
        Manoj Malviya <manojmalviya@...lsio.com>,
        Santosh Rastapur <santosh@...lsio.com>,
        "yuval.mintz@...gic.com" <yuval.mintz@...gic.com>,
        "odedw@...lanox.com" <odedw@...lanox.com>,
        "ariela@...lanox.com" <ariela@...lanox.com>,
        "galp@...lanox.com" <galp@...lanox.com>,
        "Kirsher, Jeffrey T" <jeffrey.t.kirsher@...el.com>
Subject: RE: [PATCH net-next 1/3] net: ethtool: add support for forward
 error correction modes

> -----Original Message-----
> From: netdev-owner@...r.kernel.org [mailto:netdev-
> owner@...r.kernel.org] On Behalf Of Jakub Kicinski
> Sent: Thursday, July 06, 2017 12:02 PM
> To: Casey Leedom <leedom@...lsio.com>
> Cc: Dustin Byford <dustin@...ulusnetworks.com>; Andrew Lunn
> <andrew@...n.ch>; Roopa Prabhu <roopa@...ulusnetworks.com>;
> davem@...emloft.net; linville@...driver.com; netdev@...r.kernel.org;
> vidya.chowdary@...il.com; olson@...ulusnetworks.com; Manoj Malviya
> <manojmalviya@...lsio.com>; Santosh Rastapur <santosh@...lsio.com>;
> yuval.mintz@...gic.com; odedw@...lanox.com; ariela@...lanox.com;
> galp@...lanox.com; Kirsher, Jeffrey T <jeffrey.t.kirsher@...el.com>
> Subject: Re: [PATCH net-next 1/3] net: ethtool: add support for forward error
> correction modes
> 
[..]
> > In our discussions of the above, we decided that we should err in the
> > direction of the absolutely simplest abstraction model, even when
> > that might result in a failure to establish a link.  Our feeling was
> > that doing anything else would result in endless user confusion.
> > Basically, if it takes longer than a simple paragraph to explain,
> > you're probably doing the wrong thing.  So, we decided that if a user
> > sets up a particular FEC setting, we keep that regardless of conflict
> > with different Transceiver Modules.  (But flag such issues in the
> > System Log in order to try to give the user a chance to understand
> > what the new cable they plugged in wasn't working.)
> 
> IMHO if something gets replugged all the settings should be reset.
> I feel that it's not entirely unlike replugging a USB adapter.  Perhaps
> we should introduce some (devlink) notifications for SFP module events
> so userspace can apply whatever static user config it has?

This is an interesting dichotomy and we've been trying to resolve it as well as the module variations and permutations grow.  I agree with Casey that this bleeds into link speeds as well.  

I can see both perspectives:  try to apply to user settings even if they do something dumb and notify if things go bad; and, swapping modules should reset.  Notifications of some kind would help the devices manage this.  We tend to go with timers today.

Carolyn

Carolyn Wyborny 
Linux Development 
Networking Division 
Intel Corporation