[openib-general] multicast code/merge status

[Hal Rosenstock]

On Tue, 2007-01-09 at 13:06, Sean Hefty wrote:
> > My thought re this was that since the rest of the original patch 
> > sequence specifically the rdma_cm UDP and ucma code are merged in 
> > 2.6.20-rcX which is the code OFED 1.2 is based on, the easy path for you 
> > would be to stage the multicast code for upstream push to 2.6.21 and 
> > then push the code as to OFED 1.2, what do you think?
> 
> I think shooting for 2.6.21 is fine, but...
> 
> > Other then that, as we discussed in SC06 there are some changes that 
> > need to be integrated in the code to allow for interoperability between 
> > a multicast rdma cm based app to IPoIB, specifically removing the RDMA 
> > CM signature from the mgid which generated from the ip addr and pkey, 
> > but not only.
> 
> ...I have not completed these changes yet.  Specifically, I have not added a 
> send only join parameter or changed the qkey.
> 
> I have also not full examined an issue where the SM log fills up with bad 
> multicast join requests.

Are these send only joins ? If so, it is because the group does not yet
exist (you need a receiver first or it to be precreated). The later is
problematic for dynamic IPmc groups.

> > The second change is related to the qkey, looking in the current code
> > of cma_join_ib_multicast() (at the multicast-sa_cache branch of the 
> > rdma-dev git) i see that the qkey is the mc ip address, which is not 
> > consistent with what librdmacm is assuming (0x1234567 etc).
> 
> This is a bug in the kernel code.  It should be using the standard qkey of 
> 0x12345678 - for now anyway.

Where does this standard qkey come from ? (I missed it).

-- Hal

> > Anyway, what we need here is to plug into the scheme of ipoib which uses 
> >   the qkey associated with the ipv4 broadcast multicast group. It turns 
> > out that there is some twilight zone here which i am working to 
> > understand better. You can see that for the ipv4 brd group ipoib lets 
> > the SM to allocate the group and qkey (ie the create param of 
> > ipoib_mcast_join is zero), i will give it some thought and let you know 
> > how i think the rdma cm can plug into this scheme, will be happy to get 
> >   other ideas as well.
> 
> The rdma_cm knows the qkey that ipoib uses before it joins a multicast group. 
> See cma_join_ib_multicast() - call to ib_sa_get_mcmember_rec().
> 
> - Sean
> 
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