1024 Chickens

Re-purposing GPUs to solve a certain class of compute problems.


Seymour Cray once said “If you were plowing a field, which would you rather use? Two strong oxen or 1024 chickens?” Seymour was comparing using two supercomputers to using a large cluster of networked microprocessors for computation. Since Seymour was the father of supercomputing, you can guess which he would choose. I’d answer him “it depends.”

So far in this blog, I’ve talked about things with which I have fairly extensive experience. I’m going to go out on limb here and talk about something I’ve never actually programmed (yet): using GPUs as computer processors. Today, these devices are certainly used as processors in the same sense that microprocessors, FPGAs and embedded microcontrollers are used as processors. I did not want to leave GPUs out of the discussion, even when I have only a theoretical understanding of them.

GPU stands for “Graphics Processing Unit.” For many years this device was the thing in your computer that created the images on your computer screen. It started off existence as an application-specific device to assist a microprocessor with displaying graphics. You see, once upon a time, a computer display was text-only. No windows, graphics, images, mouse pointer, nothing. Text. Humble beginnings, no? A microprocessor acting alone could not do its usual general purpose thing and do graphical work at the same time. So GPUs were created to offload the graphics work from the microprocessor, which leads to why your computer desktop has images and icons and windows and whatnot.

When microprocessor performance hit a brick wall a few years ago, some clever people realized the GPU could be used to solve a certain class of processing problems. A single GPU consists of thousands of moderately powerful graphics instruction processors, each executing the same set of program instructions on different sets of data. Look at your computer screen and imagine it is divided into many independent regions of graphics data. All of the independent regions of graphics data have common image processing instructions performed on them, like shading, blending, interpolation and the like. The data is different, the instructions are the same. Some application programs display these characteristics in that they have to do the same thing over an enormous amount of independent chunks of data. Massive parallel execution, as long as each moderately powerful graphics instruction processor in a GPU is executing the same program on different independent sets of data. So maybe 1024 chickens is better than two strong oxen for certain types of problems. No surprising, really, as a hammer is great for certain problems while a socket wrench is great for other types of problems. This is why we have microprocessors, FPGAs, embedded microcontrollers and GPUs used as processors. It always depends on the problem you’re trying to solve.

Author: David Pointer

Pragmatic programmer. Consilient alchemist. Pro geek. Serial hobbyist. Miniature tabletop gamer.

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