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From: Galen Shipman (gshipman_at_[hidden])
Date: 2007-06-13 11:38:21


Hi Gleb,

As we have discussed before I am working on adding support for
multiple QPs with either per peer resources or shared resources.
As a result of this I am trying to clean up a lot of the OpenIB code.
It has grown up organically over the years and needs some attention.
Perhaps we can coordinate on commits or even work from the same temp
branch to do an overall cleanup as well as addressing the issue you
describe in this email.

I bring this up because this commit will conflict quite a bit with
what I am working on, I can always merge it by hand but it may make
sense for us to get this all done in one area and then bring it all
over?

Thanks,

Galen

On Jun 13, 2007, at 7:27 AM, Gleb Natapov wrote:

> Hello everyone,
>
> I encountered a problem with openib on depend connection code.
> Basically
> it works only by pure luck if you have more then one endpoint for
> the same
> proc and sometimes breaks in mysterious ways.
>
> The algo works like this: A wants to connect to B so it creates QP
> and sends it
> to B. B receives the QP from A and looks for endpoint that is not
> yet associated
> with remote endpoint, creates QP for it and sends info back. Now A
> receives
> the QP and goes through the same logic as B i.e looks for endpoint
> that is not
> yet connected, BUT there is no guaranty that it will find the
> endpoint that
> initiated the connection in the first place! And if it finds
> another one it will
> create QP for it and will send it back to B and so on and so forth.
> In the end
> I sometimes receive a peculiar mesh of connection where no QP has a
> connection
> back to it from the peer process.
>
> To overcome this problem B needs to send back some info that will
> allow A to
> determine the endpoint that initiated a connection request. The
> lid:qp pair
> will allow for this. But even then the problem will remain if two
> procs initiate
> connection at the same time. To dial with simultaneous connection
> asymmetry
> protocol have to be used one peer became master another slave.
> Slave alway
> initiate a connection to master. Master choose local endpoint to
> satisfy
> incoming request and sends info back to a slave. If master wants to
> initiate a
> connection it send message to a slave and slave initiate connection
> back to
> master.
>
> Included patch implements an algorithm described above and work for
> all
> scenarios for which current code fails to create a connection.
>
> --
> Gleb.
> <fix_openib_wireup.diff>
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