Reaching a decision

English: Distributed Memory
English: Distributed Memory (Photo credit: Wikipedia)

A week further on and not much C++ has been written – and now I think I need to make a new start.

Up to this point I have been trying to write a software model of the hardware and my thought was I could think put a software-modelling layer on top of that. But that simply is not going to work – it is just too complex.

Instead I am going to have to make some policy decisions in the software – essentially over how I model the local memory on the chip: each tile will process memory reads and writes and needs to know where that memory is – it could be in the global off-chip memory store or it could be on-chip.

The difference matters because, at least in theory, the on-chip memory is speedily accessible, while the off-chip memory is 50 to 100 to 500 times “further away”. ¬†Because memory accesses exhibit locality it makes sense to ship blocks of addressed memory from the global to the local store – but doing so takes time and if there are a lot of memory movements then we get thrashing.

What I now have to do is think of what policy I will use to decide what memory gets stored locally (or, more likely, what policy I use to map the addresses). I’ll start by once again reviewing papers that propose some schemes for existing Networks-on-Chip.

In other news: I have had a paper (of which I am co-author and first named author) accepted by OSPERTS 15 – so I will be off to Sweden to get mauled by the audience there in early July. It will be an experience, and I am looking forward to it, but I also think it might be not so much a baptism, but a destruction by fire.