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From: George Bosilca (bosilca_at_[hidden])
Date: 2006-02-08 19:41:00


On Feb 8, 2006, at 7:06 PM, Jean-Christophe Hugly wrote:

> But should I understand from all this that the "direct" mode will
> never
> actually work ? It seems that if you need at least two transports,
> then
> none of them can be the hardwired unique one, right ? Unless there's a
> built-in switch between a built-in self and the built-in other
> transport.

Some of the transport layers are able to handle the messages to
"self". However, as we decide to let "self" do this type of work no
effort was spending on making sure they do it. Our first concern was/
is/will be about performance, and "self" really do a great job. So
the quick answer to your question is no, there is no way to limit the
number of transports to one.

Long ago, before the latest version of the BTL (byte transport
layer), we had something called the PTL. They were used with another
set of PML (protocol management layer). I wrote a specific PML
(called uniq) that was able to handle only one device (plus "self").
The latency went down by a little bit (around 0.3 micro-seconds).
Anyway, the old openib PTL never reached a stable state so this will
not help you :(. As we plan to drop all support for the old
generation of PML/PTL, I don't think is a wise idea to spend time on
the openib PTL to make it working with uniq ...

   Thanks,
     george.

"Half of what I say is meaningless; but I say it so that the other
half may reach you"
                                   Kahlil Gibran