> On 23 Apr 2018, at 21:16, jackm <ja...@dev.mellanox.co.il> wrote:
>
> On Mon, 23 Apr 2018 16:19:57 +0200
> Håkon Bugge <haakon.bu...@oracle.com> wrote:
>
>
>>>
>>> This actually looks like a genuine bug, why is it described only as
>>> 'confusing'? ib_register_mad_agent is callable from userspace, so at
>>> least two userspace agents can race and get the same TID’s.
>>
>> My understanding is that every lookup is using the {port, TID} tuple.
>> As such, it is not a bug, but, very confusing.
> Haakon, you are correct (see snippet from the IB spec, below).
>
> We will NOT have a situation where there are 2 threads/apps
> with the same agent ID on the *same port* (accessing the agent ID
> allocator is protected by a per-port spinlock). Having the same agent ID
> on DIFFERENT ports is OK.
> Thus, there is NO bug here. (But as Haakon says, IMHO it is more robust
> to avoid having the same agent ID for 2 agents even if those agents are
> on different ports).
>
>>
>>> TIDs need to be globally unique on the entire machine.
>>
> Jason, that is not exactly correct.
>
> From the IB Spec 1.3, C13-18.1.1 (in section 13.4.6.4 - TransactionID
> usage):
> "When initiating a new operation, MADHeader:TransactionID
> shall be set to such a value that within that MAD the combination of
> TID, SGID, and MgmtClass is different from that of any other currently
> executing operation. If the MAD does not have a GRH, its SLID is used
> in the combination in place of an SGID."
>
> Since the SGID/SLID is different for each port, the per-port guarantee
> of no 2 agents receiving the same agent-ID value is sufficient.
>
> -Jack
Shall I interpret this silence as my commit is good to go or that I should add
Jack’s tangible information to the commit message?
Thxs, Håkon
