4 ms·

I don't want to worry you, but on a mobile device with a screen the GPU is always spinning. That is where the pixels come from after all. I get your point that

I don't want to worry you, but on a mobile device with a screen the GPU is always spinning. That is where the pixels come from after all. I get your point that there are energy efficiency tradeoffs to consider. However for massively data parallel tasks like image operations, 3d graphics, machine learning, vision etc, I haven't seen SIMD implementation come close to GPU compute in terms of efficiency. Perhaps short lived text pressing and file compression where data access is more random could benefit from SIMD.

vvanders 8y ago
Nope, I'm well aware. Built/worked on two android based 3D graphics stacks at two different companies and I've worked directly with just about every mobile GPU vendor aside from PowerVR(which is pretty similar to all the other tiled GPUs that are out there). Your GPU is actually running much less than you'd expect. Unless pixels are changing there's a 95% chance that everything on the system is sleeping and just the display controller is being kept spun up. Battery requirements mean that DVCS on any mobile chipset is going to be really aggressive. Either way GPU compute has a pretty large overhead both in terms of latency and scheduling. Earlier GPUs didn't schedule nice(hello waiting 16.6ms for your next compute request) and generally the type of places where you use SIMD(3D transforms, audio processing, etc) are so tightly coupled with other CPU operations that even the act of moving them to the SIMD registers is something you need to consider before diving into it. A lot of times waiting for some work queue to complete(or adding pipeline latency by waiting for next frame) just isn't feasible.
jononor 8y ago
The screen of a mobile device is off just as much (or more) as it is on. More and more processing is happening in the background, when user is not actively doing something.
stefan_ 8y ago
Pixels on screen come from the display controller, which on mobile is often a distinct piece of IP from the GPU, unlike desktop systems. Scenarios like watching a video full screen can often happen without GPU involvement at all.

vvanders 8y ago

Nope, I'm well aware. Built/worked on two android based 3D graphics stacks at two different companies and I've worked directly with just about every mobile GPU vendor aside from PowerVR(which is pretty similar to all the other tiled GPUs that are out there). Your GPU is actually running much less than you'd expect. Unless pixels are changing there's a 95% chance that everything on the system is sleeping and just the display controller is being kept spun up. Battery requirements mean that DVCS on any mobile chipset is going to be really aggressive. Either way GPU compute has a pretty large overhead both in terms of latency and scheduling. Earlier GPUs didn't schedule nice(hello waiting 16.6ms for your next compute request) and generally the type of places where you use SIMD(3D transforms, audio processing, etc) are so tightly coupled with other CPU operations that even the act of moving them to the SIMD registers is something you need to consider before diving into it. A lot of times waiting for some work queue to complete(or adding pipeline latency by waiting for next frame) just isn't feasible.

jononor 8y ago

The screen of a mobile device is off just as much (or more) as it is on. More and more processing is happening in the background, when user is not actively doing something.

stefan_ 8y ago

Pixels on screen come from the display controller, which on mobile is often a distinct piece of IP from the GPU, unlike desktop systems. Scenarios like watching a video full screen can often happen without GPU involvement at all.