netdev - RE: [PATCH net-next 4/4] bonding: allow carrier and link status to determine link state

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Message-ID: <5efd353b7f6e4e9595342f18ba42fefd@usma1ex-dag1mb2.msg.corp.akamai.com>
Date:   Mon, 14 May 2018 17:39:27 +0000
From:   "Banerjee, Debabrata" <dbanerje@...mai.com>
To:     'Jay Vosburgh' <jay.vosburgh@...onical.com>
CC:     "David S . Miller" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Veaceslav Falico <vfalico@...il.com>,
        "Andy Gospodarek" <andy@...yhouse.net>
Subject: RE: [PATCH net-next 4/4] bonding: allow carrier and link status to
 determine link state

> From: Jay Vosburgh [mailto:jay.vosburgh@...onical.com]
> Debabrata Banerjee <dbanerje@...mai.com> wrote:
> 
> >In a mixed environment it may be difficult to tell if your hardware
> >support carrier, if it does not it can always report true. With a new
> >use_carrier option of 2, we can check both carrier and link status
> >sequentially, instead of one or the other
> 
> 	What do you mean by "mixed environment," and under what
> circumstances are you seeing an actual benefit from doing the MII / ethtool
> test in addition to the standard netif_carrier_ok test?
> 
> 	The use_carrier option was meant for backwards compatibility with
> old-in-2005 device drivers, so this seem counterintuitive to me.  I don't recall
> seeing any devices lacking netif_carrier support for some time.  At this point,
> I would tend to argue that a new device driver that does not implement
> netif_carrier support should be fixed, and not have another hack added to
> bonding to work around it.

Mixed environment = 100k machines with dozen NIC flavors. I have logs of a bnx2x machine that was reporting carrier OK with speed and duplex as unknown. Led to some interesting behavior of flooding on the switch due to the local destination mac not being known by the switch. Of course these situations get rectified manually, and if they don't happen again it's hard for me to confirm details of how it broke. However, while we continue to have both checks, it would make sense to be able to use both. If it's reliable enough to use carrier only, then it can go away. We could carry this patch internally for the time being, but it seemed useful for everyone. See below:

Bonding Mode: adaptive load balancing
Primary Slave: None
Currently Active Slave: ith1
MII Status: up
MII Polling Interval (ms): 100
Up Delay (ms): 0
Down Delay (ms): 0

Slave Interface: ith0
MII Status: up
Speed: 10000 Mbps
Duplex: full
Link Failure Count: 1
Permanent HW addr: 00:e0:81:e5:0e:16
Slave queue ID: 0

Slave Interface: ith1
MII Status: up
Speed: Unknown
Duplex: Unknown
Link Failure Count: 0
Permanent HW addr: 00:e0:81:e5:0e:18
Slave queue ID: 0