Re: [Gems-users] The Network in Ruby

[Mike Marty <mikem@xxxxxxxxxxx>]

> I am trying to do something with the interconnect in Ruby, but I have 
> encountered some problems:
> 1. What's the difference between intra-chip and inter-chip networks? 
> There are 4 "auto-generated" networks in Ruby, but the tutorial says 
> they are used in "inter-chip". If I just simulate a single chip with 8 
> processors, is there any "inter-chip"  network?
"inter-chip" is supposed to mean off-chip network.  "intra-chip" means 
on-chip network. 

>     According to the Figure of Ruby, seems that there is only one 
> network connecting all the components including L1s, L2 banks and 
> directories which are the memories. So I guess the interconnect treats 
> all the components equally and connects them with switches and links. 
> If so, how does it distinguish intra-chip or inter-chip? Meaning, does 
> it apply the different parameters ( e.g. ON_CHIP_LINK_LATENCY, 
> NETWORK_LINK_LATENCY) to different links as those links may be intra- 
> or inter- chip?
Yes, the interconnect is the same with different link latencies and 
bandwidth parameters for off-chip links.
> 2. About the 4 auto-generated networks, I have run a checkpoint 
> loading Ruby with each of them for 1000000 SIMICS cycles, and I've got 
> different results. For the link latency, CROSSBAR has a constant 
> latency 152 between each pair of components, while HIERARCHICAL_SWITCH 
> has a constant latency of 356. Why does HIERARCHICAL_SWITCH also have 
> a constant latency? Is it because all the packets have to go through 
> the root switch even though the source and destination are neighbours?
Yes
>     In PT_TO_PT, the latencies may be 3, 52 or 101 because of the 
> different on-chip and off-chip latencies set in rubyconfig.defaults, 
> but the TORUS_2D has the exactly same latency of each component 
> pair with PT_TO_PT, why?
>  
Where are you getting these latencies?
> 3. I also set g_PRINT_TOPOLOGY true to see the results in the 
> output file. PT_TO_PT has a switch0 with 48 in-links and 48 out-links, 
> a switch1 with 1 in-link and 1 outlink, and switch2 to switch 31 with 
> 0 in-link and 0 out-link. How can I understand this? Also, TORUS_2D 
> has a switch0 with 52 in-links and 52 out-links, but switch1 to switch 
> 15 each has 4 in-links and 4 out-links, why? Is there anyway I can 
> understand the built-in topologies easier?
>  
All the Topology code is in ruby/network/simple/Topology.C

You might try using the FILE_SPECIFIED topology in order to create what 
you want and understand.
--Mike