Re: [RFC] XRC upstream merge reboot

Jack Morgenstein
2011-06-23T06:35:07Z

On Wednesday 22 June 2011 22:57, Hefty, Sean wrote:
> > > We can report the creation of a tgt qp on an xrcd as an async event.
> > To whom?
>
> to all users of the xrcd.  IMO, if we require undefined, out of band communication to use
> XRC, then we have an incomplete solution.  It's just too bad that we can't report additional
> data (like the tgt qpn) with an async event...
>
I do not think this will help much. Just knowing that a TGT QP exists is not really relevant. The sender (who is on a remote host)
needs to know about the TGT QP, to use it to send to the XRC SRQs. We cannot propagate an event over to the sender side! The local users
of the TGT QP don't really care -- it is the responsibility of the Application to get the INI-TGT linkage up, and the XRC SRQs created before
sending from INI to SRQ. At that point, the SRQ either receives packets or it does not.

I do agree, though, that the need to use out-of-band communication (rather than the CM) to establish the INI-TGT RC connection is not clean.

If you are thinking of using this for tracking, there is no way that I can see except reference counting to know when all users of the TGT have
finished with it. Indicating usage by "tapping" the TGT QP whenever an SRQ receives a packet via the TGT is not a good idea (this is data
path!), not to mention that quiescence is not a good indicator of whether an app is done using the target (the amount of time that things
are quiet depends on the app).

We discussed using a "heartbeat" in the thread link I sent you, and ultimately discarded that idea.

If you have other ideas which you think might work, please send them along.

-Jack