My post on SiCS multicore, as well as the SiCS multicore day itself, put a renewed spotlight on the GPGPU phenomenon. I have been following this at a distance, since it does not feel very applicable to neither my job of running Simics, nor do I see such processors appear in any customer applications. Still, I think it is worth thinking about what a GPGPU really is, at a high level.
The Radio Register has a nice interview with Kunle Olukotun, the man most known for the Afara/Sun Niagara/UltraSparc T1-2-etc. design. It is a long interview, lasting well over an hour, but it is worth a listen. A particular high point is the story on how Kunle worked on parallel processors in the mid-1990s when everyone else was still chasing single-thread performance. He really was a very early proponent of multicore, and saw it coming a bit before most other (general-purpose) computer architects did. Currently, he is working on how to program multiprocessors, at the Stanford Pervasive Parallelism Laboratory (PPL). In the interview, I see several themes that I have blogged about before being reinforced…
An old colleague just sent me an email bringing up a discussion we had last year, where he was a strong proponent for the homogeneous model of a multiprocessor. The root of that discussion was the difference between the Xbox 360 and Playstation 3 processors. The Xbox 360 has a three-core, two-threads-per-core homogeneous PowerPC main processor called the Xenon (plus a graphics processor, obviously), while the PS3 has a Cell processor with a single two-threaded PowerPC core and seven SPEs, Synergistic Processing Elements (basically DSP-like SIMD machines).
In the game business, it is clear that the Xenon CPU is considered easier to code for. This means that even though the Cell processor clearly has higher theoretical raw performance, in practical the two machines are about equal in power since it is harder to make use of the Cell. Which seems to be a fact.
So here, homogeneous systems do appear to have it easier among programmers. However, I do not believe that that extends to all systems, all the time, everywhere.