In a post from late June, Jeff Atwood at Coding Horror discusses the horrible cost of a large HP server (scaling up to 32 processor cores in eight AMD x86 sockets), compared to a bunch of simple single-socket basic servers. There are some interesting notes on relative costs of small-and-simple servers, including things like administration and power. There is an undercurrent to the post and the comments that the big HP machine is “overpriced”. I don’t think it is. If you have ever had Erik Hagersten as a teacher in computer architecture, you will know why.
A common question from simulation users to us simulation providers is “can I simulate a machine with N cores”, where N is “large”. As if running lots of cores was a simulation system or even a hardware problem. In almost all cases, the problem is with software. Creating an arbitrary configuration in a virtual platform is easy. Creating a software stack for that arbitrary platform is a lot harder, since an SMP software stack needs to understand about the cores and how they communicate.
Essentially, what you need is a hardware design that has addressing room for lots of cores, and a software stack that is capable of using lots of cores — even if such configurations do not exist in hardware. Unfortunately, since software is normally written to run on real existing machines, there tends to be unexpected limitations even where scalability should be feasible “in principle”.
Here is the story of how I convinced Linux to handle more than two cores in a virtual MPC8641D machine.
In a funny coincidence, I published an article at SCDSource.com about the need for cycle-accurate models for virtual platforms on the same day that ARM announced that they were selling their cycle-accurate simulators and associated tool chain to Carbon Technology. That makes one wonder where cycle-accuracy is going, or whether it is a valid idea at all… is ARM right or am I right, or are we both right since we are talking about different things?
Let’s look at this in more detail.
The SICS Multicore Day August 31 was a really great event! We had some fantastic speakers presenting the latest industry research view on multicores and how to program them. Marc Tremblay did the first presentation in Europe of Sun’s upcoming Rock processor. Tim Mattson from Intel tried hard to provoke the crowd, and Vijay Saraswat of IBM presented their X10 language. Erik Hagersten from Uppsala University provided a short scene-setting talk about how multicore is becoming the norm.