Re: [Gems-users] crossbar

[Mike Marty <mikem@xxxxxxxxxxx>]

> I would like to have a better understanding of the crossbar model using the
> MSI_MOSI_CMP_directory protocol. I did a simulation with 4
> processor-configuration.
>
> Firstly, under "Network Configuration" it states that the network is a
> SIMPLE_NETWORK and that the topology is a CROSSBAR. However, a number of
> virtual_net_0/1/2/3/4 are mentioned that are either ordered or unordered.
> Could you give a brief explanation of what this is and why some are ordered
> and others unordered? What does it mean that a virtual_net is
> ordered/unordered?
>

The ordered="true" property enforces point-to-point ordering regardless of
the underlying topology.  If the underlying topology is ordered, then this
option has no effect.

> Secondly, statistics show (under "Network stats") utilization for switch_0
> until switch_12, so there are 13 (0 until 12) switches in total. It seems
> like there is one top-switch (Nr 12) that all are connected to, right? Does
> this mean that there is a hierarchy? I fail to understand how these switches
> are organized from a topology point of view. Is 13 switches really needed to
> connect 4 processors and L2? If yes, could you explain how they are
> used/connected?
>

There is a switch at the endpoint of each processor and a switch at the
endpoint of each L2 bank.  Then there are the internal interconnect
switches dependent on topology.

> A final side note, I saw that the final four data from the last switch only
> specified Control stats, whereas the rest of the switches had both Data and
> Control. Is there a reason for this?
>

Without seeing more info, I'm not sure

--Mike