On Thu, 26 Apr 2018 18:06:10 +0200 Håkon Bugge <[email protected]> wrote:
> > On 23 Apr 2018, at 21:16, jackm <[email protected]> wrote: > > > > On Mon, 23 Apr 2018 16:19:57 +0200 > > Håkon Bugge <[email protected]> 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? > > Haakon, I think Jason is on vacation this week. Best to wait for his response. -Jack > Thxs, Håkon >
