Message-ID: <CAGVrzcY=hxAf0eOoDfAAQZS1fNjFWbdY9Nbyuz6kFaOkSSis8w@mail.gmail.com>
Date:	Thu, 27 Mar 2014 14:20:06 -0700
From:	Florian Fainelli <f.fainelli@...il.com>
To:	Sergey Ryazanov <ryazanov.s.a@...il.com>
Cc:	Jiri Pirko <jiri@...nulli.us>, Jamal Hadi Salim <jhs@...atatu.com>,
	Roopa Prabhu <roopa@...ulusnetworks.com>,
	Neil Horman <nhorman@...driver.com>,
	Thomas Graf <tgraf@...g.ch>, netdev <netdev@...r.kernel.org>,
	David Miller <davem@...emloft.net>,
	Andy Gospodarek <andy@...yhouse.net>,
	dborkman <dborkman@...hat.com>, ogerlitz <ogerlitz@...lanox.com>,
	jesse <jesse@...ira.com>, pshelar <pshelar@...ira.com>,
	azhou <azhou@...ira.com>, Ben Hutchings <ben@...adent.org.uk>,
	Stephen Hemminger <stephen@...workplumber.org>,
	jeffrey.t.kirsher@...el.com, vyasevic <vyasevic@...hat.com>,
	Cong Wang <xiyou.wangcong@...il.com>,
	John Fastabend <john.r.fastabend@...el.com>,
	Eric Dumazet <edumazet@...gle.com>,
	Scott Feldman <sfeldma@...ulusnetworks.com>,
	Lennert Buytenhek <buytenh@...tstofly.org>,
	Shrijeet Mukherjee <shm@...ulusnetworks.com>,
	Felix Fietkau <nbd@...nwrt.org>
Subject: Re: [patch net-next RFC 0/4] introduce infrastructure for support of
 switch chip datapath

2014-03-27 13:32 GMT-07:00 Sergey Ryazanov <ryazanov.s.a@...il.com>:
> 2014-03-27 20:41 GMT+04:00 Florian Fainelli <f.fainelli@...il.com>:
>> 2014-03-27 7:10 GMT-07:00 Sergey Ryazanov <ryazanov.s.a@...il.com>:
>>> Hi all,
>>>
>>> sorry for the intrusion, but let me place my 2 cents.
>>>
>>> 2014-03-27 10:56 GMT+04:00 Jiri Pirko <jiri@...nulli.us>:
>>>> Wed, Mar 26, 2014 at 11:22:51PM CET, f.fainelli@...il.com wrote:
>>>>>2014-03-26 14:51 GMT-07:00 Jamal Hadi Salim <jhs@...atatu.com>:
>>>>>> On 03/26/14 14:14, Jiri Pirko wrote:
>>>>>>>
>>>>>>> Wed, Mar 26, 2014 at 06:58:32PM CET, f.fainelli@...il.com wrote:
>>>>>>>>
>>>>>>>> 2014-03-26 10:35 GMT-07:00 Jiri Pirko <jiri@...nulli.us>:
>>>>>>
>>>>>>
>>>>>>
>>>>>>>> You are right, sw1p0 and sw1p1 were meant to be, say LAN ports in my
>>>>>>>> example.
>>>>>>>>
>>>>>>>> I think there is an implicit convention that sw1 represents the
>>>>>>>> Ethernet switch port connected to the CPU Ethernet MAC, and that it is
>>>>>>>> always connected, hence there is no need to create a "fake" bridge to
>>>>>>>> link sw1 to eth0 for instance?
>>>>>>>
>>>>>>>
>>>>>>> I think you are kind of mixing apples and oranges (or I might be I'm not
>>>>>>> understanding you correctly).
>>>>>>> This is how I see it, sticking to the names you use in the example:
>>>>>>>
>>>>>>>              (sw1) (abstract place-holder netdev)
>>>>>>>            --------
>>>>>>>           switch chip                   CPU
>>>>>>>     -----------------------            ------
>>>>>>>     sw1p0 sw1p1 sw1p2 sw1p3             eth0
>>>>>>>       |     |     |     |                |
>>>>>>>      PHY   PHY   PHY    ------someMII-----
>>>>>>>
>>>>>>> You see that eth0 is the CPU part of the "connection" and sw1p3 is the
>>>>>>> switch part (port representation).
>>>>>>>
>>>>>>
>>>>>>
>>>>>> Florian - I am sure you explained this before; I just dont remember. Why
>>>>>> is there need to expose eth0? It seems to me sw1p0-3 are abstracted
>>>>>> already in the kernel and the "cpu port" is merely a control interface.
>>>>>
>>>>>eth0 corresponds to a CPU Ethernet MAC facing e.g: sw1p3 switch port.
>>>>>It is "regular" Ethernet driver connected to the switch without
>>>>>switch-specific logic. The goal is twofold:
>>>>>
>>>>>- allow any regular Ethernet driver to be connected to an external
>>>>>switch via e.g: MDIO/MDC or other without specific switch knowledge
>>>>>- represents accurately how the hardware is designed/connected
>>>>>
>>>>>but maybe, we can simplify and have e.g: sw1p3 and eth0 be the same interface...
>>>>
>>>> I believe that hawing both sw1p3 and eth0 is the correct way of
>>>> modelling this. sw1p3 is instance if switch chip driver representing the
>>>> actual port of a switch. eth0 is an instance of some other ordinary NIC
>>>> driver (8139too is my favorite :))
>>>>
>>>> This model allows to draw the exact picture.
>>>> Also, when you add the described possibility to use iplink to build
>>>> vlans, bridges whatever on the switch ports, it makes perfect sense to
>>>> have this model.
>>>>
>>>> Merging sw1p3 and eth0 would cause a loose of information and confusion.
>>>>
>>>
>>> CPU switch port and switch fabric itself should be configured in
>>> consistence with host, in first place I mean a set of VLANs. Also it
>>> should be mentioned that some generic knobs such as port rate and
>>> duplex mode are meaningless for CPU switch port and a lot of status
>>> information (rx/tx counters etc.) duplicates statistics of host
>>> interface which is connected to switch port.
>>
>> It duplicates the information when things just work fine, consider an
>> external switch connected via RGMII to a CPU Ethernet MAC, you might
>> want to get statistics from both sides (the switch CPU port and the
>> CPU Ethernet MAC) to diagnose why things are not working as expected,
>> which unfortunately happens once in a while with RGMII.
>>
>> If we expose both net_device, we will be able to retrieve statistics
>> about from both sides, without resorting to ad-hoc debugging tools,
>> but maybe this is not worth the effort.
>>
> I also thought about this situation. Can we use the debugfs interface
> for these purposes?

Most of the time you are interesting in MIB counters for debugging
such issues, so ethtool quickly comes handy for this task. Since we
will provide per-port counters, the CPU port is not different, so
there are no reason for restricting this.

>
>>> So there are no reasons
>>> to force user to configure this port manually, and automatic
>>> configuration of CPU switch port without exporting them as netdev
>>> seems as good approach.
>>
>> Well, maybe that's the answer, since we know that e.g: sw1p3 is always
>> connected to e.g: eth0, we could create an automatic bridge between
>> those two, this would keep the netdev exposure to user-space, but an
>> user would not have to know about that specific detail to get things
>> to work.
>>
> I would like go further and suggest to consider a netdev that is
> connected to the CPU switch port, as master. In case when we need to
> perform some action on whole switch (e.g. dump FIB).

This is what the 'sw1' net_device in Jiri's proposal would do.

> And even name
> switch ports, using master netdev name as prefix (e.g. eth1p0, eth1p1,
> ..., eth1pN for ports of switch that is connected via eth1).

I think the port naming using the switch abstract interface (sw1 here)
is better because ports do belong to the switch.
-- 
Florian
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