“It has a completely different instruction set than Pascal,” remarked Bryan Catanzaro, vice president, Applied Deep Learning Research at Nvidia. “It’s fundamentally extremely different. Volta is not Pascal with Tensor Core thrown onto it – it’s a completely different processor.”
Catanzaro, who returned to Nvidia from Baidu six months ago, emphasized how the architectural changes wrought greater flexibility and power efficiency.
“It’s worth noting that Volta has the biggest change to the GPU threading model basically since I can remember and I’ve been programming GPUs for a while,” he said. “With Volta we can actually have forward progress guarantees for threads inside the same warp even if they need to synchronize, which we have never been able to do before. This is going to enable a lot more interesting algorithms to be written using the GPU, so a lot of code that you just couldn’t write before because it potentially would hang the GPU based on that thread scheduling model is now possible. I’m pretty excited about that, especially for some sparser kinds of data analytics workloads there’s a lot of use cases where we want to be collaborating between threads in more complicated ways and Volta has a thread scheduler can accommodate that.
“It’s actually pretty remarkable to me that we were able to get more flexibility and better performance-per-watt. Because I was really concerned when I heard that they were going to change the Volta thread scheduler that it was going to give up performance-per-watt, because the reason that the old one wasn’t as flexible is you get a lot of energy efficiency by ganging up threads together and having the capability to let the threads be more independent then makes me worried that performance-per-watt is going to be worse, but actually it got better, so that’s pretty exciting.”
Added Alben: “This was done through a combination of process and architectural changes but primarily architecture. This was a very significant rewrite of the processor architecture. The Tensor Core part is obviously very [significant] but even if you look at FP32 and FP64, we’re talking about 50 percent more performance in the same power budget as where we’re at with Pascal. Every few years, we say, hey we discovered something really cool. We basically discovered a new architectural approach we could pursue that unlocks even more power efficiency than we had previously. The Volta SM is a really ambitious design; there’s a lot of different elements in there, obviously Tensor Core is one part, but the architectural power efficiency is a big part of this design.”