Message-ID: <22e86150-925f-0229-3d54-a7d82d504835@intel.com>
Date:   Fri, 27 Mar 2020 13:47:44 -0700
From:   "Samudrala, Sridhar" <sridhar.samudrala@...el.com>
To:     Saeed Mahameed <saeedm@...lanox.com>,
        "kuba@...nel.org" <kuba@...nel.org>
Cc:     Aya Levin <ayal@...lanox.com>,
        "andrew.gospodarek@...adcom.com" <andrew.gospodarek@...adcom.com>,
        "sburla@...vell.com" <sburla@...vell.com>,
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        Tariq Toukan <tariqt@...lanox.com>,
        "davem@...emloft.net" <davem@...emloft.net>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        Vlad Buslov <vladbu@...lanox.com>,
        "lihong.yang@...el.com" <lihong.yang@...el.com>,
        Ido Schimmel <idosch@...lanox.com>,
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        Moshe Shemesh <moshe@...lanox.com>,
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        Eran Ben Elisha <eranbe@...lanox.com>
Subject: Re: [RFC] current devlink extension plan for NICs



On 3/27/2020 12:45 PM, Saeed Mahameed wrote:
> On Fri, 2020-03-27 at 12:10 -0700, Jakub Kicinski wrote:
>> On Fri, 27 Mar 2020 11:49:10 -0700 Samudrala, Sridhar wrote:
>>> On 3/27/2020 9:38 AM, Jakub Kicinski wrote:
>>>> On Fri, 27 Mar 2020 08:47:36 +0100 Jiri Pirko wrote:
>>>>>> So the queues, interrupts, and other resources are also part
>>>>>> of the slice then?
>>>>>
>>>>> Yep, that seems to make sense.
>>>>>   
>>>>>> How do slice parameters like rate apply to NVMe?
>>>>>
>>>>> Not really.
>>>>>   
>>>>>> Are ports always ethernet? and slices also cover endpoints
>>>>>> with
>>>>>> transport stack offloaded to the NIC?
>>>>>
>>>>> devlink_port now can be either "ethernet" or "infiniband".
>>>>> Perhaps,
>>>>> there can be port type "nve" which would contain only some of
>>>>> the
>>>>> config options and would not have a representor "netdev/ibdev"
>>>>> linked.
>>>>> I don't know.
>>>>
>>>> I honestly find it hard to understand what that slice abstraction
>>>> is,
>>>> and which things belong to slices and which to PCI ports (or why
>>>> we even
>>>> have them).
>>>
>>> Looks like slice is a new term for sub function and we can consider
>>> this
>>> as a VMDQ VSI(intel terminology) or even a Queue group of a VSI.
>>>
>>> Today we expose VMDQ VSI via offloaded MACVLAN. This mechanism
>>> should
>>> allow us to expose it as a separate netdev.
>>
>> Kinda. Looks like with the new APIs you guys will definitely be able
>> to
>> expose VMDQ as a full(er) device, and if memory serves me well that's
>> what you wanted initially.
>>
> 
> VMDQ is just a steering based isolated set of rx tx rings pointed at by
> a dumb steering rule in the HW .. i am not sure we can just wrap them
> in their own vendor specific netdev and just call it a slice..
> 
> from what i understand, a real slice is a full isolated HW pipeline
> with its own HW resources and HW based isolation, a slice rings/hw
> resources can never be shared between different slices, just like a vf,
> but without the pcie virtual function back-end..

The above definition of slice matches a VMDQ VSI. It is an isolated set 
of queues/interrupt vectors/rss and packet steering rules can be added 
to steer packets from and to this entity. A PF is associated with its 
own VSI and can spawn multiple VMDQ VSIs similar to VFs.

By default a PF is associated with a single uplink port.

> 
> Why would you need a devlink slice instance for something that has only
> rx/tx rings attributes ? if we are going with such design, then i guess
> a simple rdma app with a pair of QPs can call itself a slice ..
> 
> We need a clear-cut definition of what a Sub-function slice is.. this
> RFC doesn't seem to address that clearly.
> 
>> But the sub-functions are just a subset of slices, PF and VFs also
>> have a slice associated with them.. And all those things have a port,
>> too.
>>
> 
> PFs/VFs, might have more than one port sometimes ..

Yes. When the uplink ports are in a LAG, then a PF/VF/slice should be 
able to send or receive from more than 1 port.

> 
>>>> With devices like NFP and Mellanox CX3 which have one PCI PF
>>>> maybe it
>>>> would have made sense to have a slice that covers multiple ports,
>>>> but
>>>> it seems the proposal is to have port to slice mapping be 1:1.
>>>> And rate
>>>> in those devices should still be per port not per slice.
>>>>
>>>> But this keeps coming back, and since you guys are doing all the
>>>> work,
>>>> if you really really need it..

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