linux-kernel - Re: [PATCH v6 01/26] IB/Verbs: Implement new callback query

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Date:	Tue, 28 Apr 2015 19:50:48 +0000
From:	"Dave Goodell (dgoodell)" <dgoodell@...co.com>
To:	"Hefty, Sean" <sean.hefty@...el.com>
CC:	Tom Talpey <tom@...pey.com>, Doug Ledford <dledford@...hat.com>,
	"Weiny, Ira" <ira.weiny@...el.com>,
	Michael Wang <yun.wang@...fitbricks.com>,
	"Liran Liss" <liranl@...lanox.com>,
	Roland Dreier <roland@...nel.org>,
	Hal Rosenstock <hal@....mellanox.co.il>,
	"linux-rdma@...r.kernel.org" <linux-rdma@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Steve Wise <swise@...ngridcomputing.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>,
	Tom Tucker <tom@...ngridcomputing.com>,
	Hoang-Nam Nguyen <hnguyen@...ibm.com>,
	"raisch@...ibm.com" <raisch@...ibm.com>,
	infinipath <infinipath@...el.com>, Eli Cohen <eli@...lanox.com>,
	"Latif, Faisal" <faisal.latif@...el.com>,
	"Jack Morgenstein" <jackm@....mellanox.co.il>,
	Or Gerlitz <ogerlitz@...lanox.com>,
	Haggai Eran <haggaie@...lanox.com>
Subject: Re: [PATCH v6 01/26] IB/Verbs: Implement new callback
 query_transport()

On Apr 28, 2015, at 1:14 AM, Hefty, Sean <sean.hefty@...el.com> wrote:

>>> Keep in mind that this enum was Liran's response to Michael's original
>>> patch.  In the enum in Michael's patch, there was both USNIC and
>>> USNIC_UDP.
>> 
>> Right! That's why I'm confused. Seems wrong to drop it, right?
> 
> I think the original USNIC protocol is layered directly over Ethernet.  The protocol basically stole an Ethertype (the one used for IBoE/RoCE) and implemented a proprietary protocol instead.  I have no idea how you resolve that, but I also don't think it's used anymore.  USNIC_UDP is just UDP.

Sean is correct. The legacy RDMA_TRANSPORT_USNIC code used a proprietary protocol over plain Ethernet frames.  The newer RDMA_TRANSPORT_USNIC_UDP code is just standard UDP/IP/Ethernet packets exposed to user space via the uverbs stack.  The current kernel module will support both formats, it just depends on which user space requests at create_qp time.  From the kernel point of view there is no common protocol between the two TRANSPORTs (other than sharing partially similar Ethernet frames at L2).

I posted last week to clarify some of this: http://marc.info/?l=linux-rdma&m=142972177830718&w=2

>> Well, if RoCEv2 uses the same protocol enum, that may introduce new
>> confusion, for example there will be some new CM handling for UDP encap,
>> source port selection, and of course vlan/tag assignment, etc. But if
>> there is support under way, and everyone is clear, then, ok.
> 
> RoCEv2/IBoUDP shares the same port space as UDP.  It has a similar issues as iWarp does sharing state with the main network stack.  I'm not aware of any proposal for resolving that.  Does it require using a separate IP address?  Does it use a port mapper function?  Does netdev care for UDP?  I'm not sure what USNIC does for this either, but a common solution between USNIC and IBoUDP seems reasonable.

Is the concern here about CM issues or the UDP ports used by the actual usNIC RQs?  CM is not used/supported for usNIC at this time.

-Dave

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