Clever use of Xbox One’s eSRAM could see speed gains

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FlyingMonkey

Some developers believes that the Xbox One’s included eSRAM is the second coming, while others believe it’s the bottleneck that keeps the Xbox One from performing as well as it should. According to Confetti FX’s Wolfgang Engel, the Xbox One’s eSRAM can induce great speed gains if used properly. Why should you listen to him? He happened to head up development on Rockstar’s RAGE engine; the one behind Grand Theft Auto IV, Red Dead Redemption and the very best Table Tennis game ever made.

“eSRAM is very fast memory,” he told Gamingbolt.  “In general the biggest challenge that game developers are facing are memory access patterns, so while we have a lot of computation power, the memory access cost is increasing substantially over the last ten years, compared to the cost of arithmetic instructions.

“As long as you are in registers you are fine but as soon as you need to access memory, it becomes slower. So the challenge is to access memory in the most efficient way.

“Therefore memory access patterns are the most important optimization strategies. So it’s not about counting cycles but it’s about thinking how can we re-factor an algorithm so that we can access memory in a more efficient way. eSRAM is part of that.

Theoretically, eSRAM is faster than the DDR5 Sony has used in its PlayStation 4, and if used optimally, could be used to shuttle data faster.

“For example with a compute shader you can access cache memory (thread group shared memory) so you can re-factor your algorithm so that it uses this memory better, resulting in a huge and substantial speed ups. With the Xbox One, the introduction of eSRAM has a similar idea.

“The memory expensive draw calls can be rendered into eSRAM. When you don’t need so much memory bandwidth, you use the regular system memory. You have to plan ahead, you have to think how you are going to use the memory, in the most optimal way. So eSRAM gives you an advantage if you do this. For one of our games, we used eSRAM by creating an excel sheet first, that shows how we are going to use eSRAM through the stages of the rendering pipeline. This helped us utilize the speed improvements that were coming from the eSRAM.”

It’s really sounding like the Xbox One is this generation’s PlayStation 3; a system that requires far too many little hacks and planning to get its Cell processor working working right. It likely means that multiplatform games will continue to be just that little bit worse on Microsoft’s system, until developers have built up a library of tricks and specialised skills. We may, towards the end of this generation, even see stuff on the Xbox One that couldn’t be done on the PlayStation 4. 

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Last Updated: June 2, 2014

Geoffrey Tim

Editor. I'm old, grumpy and more than just a little cynical. One day, I found myself in possession of a NES, and a copy of Super Mario Bros 3. It was that game that made me realise that games were more than just toys to idly while away time - they were capable of being masterpieces. I'm here now, looking for more of those masterpieces.

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