Re: [PATCH for-next 00/10] Add RoCE support to the mlx5 driver

[Haggai Eran <haggaie-VPRAkNaXOzVWk0Htik3J/w@public.gmane.org>]

On 25/08/2015 16:06, Achiad Shochat wrote:
> On 8/25/2015 3:32 PM, Tom Talpey wrote:
>> But I don't understand how it will work per-GID. What if the target
>> node is RoCEv2 and on another subnet? How will it discover the remote's
>> capability and establish the right protocol? How does the initiator
>> select the protocol, if there is a choice?
>>
>> Another way of asking this question is, why is all this stuff in the
>> driver, at the bottom of the stack? I think it should be in the
>> rdmacm layer.
>>
>> Tom.
>>
> 
> Selection of the RoCE version to be used per connection and discovering
> the RoCE versions supported by the target is up to the application.
> 
> It is not done by the driver of course, neither by the kernel stack.
> 
> The driver only exposes add/del_gid callbacks, used by the ib_core to
> configure the device GID table entries (including RoCE version per
> entry) based on netdev IPs configured in the system.

Let me add that when using RDMA CM, it is in charge of choosing the gid
index for a connection, and needs to be aware of the different
protocols. The patchset that includes the core changes for RoCE v2 [1]
allows configuring the preferred protocol for each port. There is also a
heuristic that selects RoCE v2 (which is routable) when the address
resolution detects more than one hop to the destination.

Regards,
Haggai

[1] http://www.spinics.net/lists/linux-rdma/msg28120.html

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