Why don't GPUs implement priorities?

[VirtualLarry]

Just wondering. When I crunch with BOINC, Collatz Conjecture project, on my GT740 1GB GDDR5, and my i3-6100, everything UI-wise lags. Not every project does this, and it doesn't lag in any way that I can notice, running Milkyway@Home on my 7950 3GB GDDR5 card, on my G4400 OCed rig, while also crunching on both CPU cores.

Thing is, I can crunch on both CPU cores, because the BOINC project app is set to a lower (background) priority, and the OS implements a priority scheme.

Yet, it seems that GPUs still don't have any notion of "this task should take priority over that task". So GPU crunching programs, lag the UI of the PC, etc.

 

[ViRGE]

They do, but it's really coarse. WDDM 2.0 and next-gen GPUs should make it better.

 

[cen1]

OS fault, not the GPU's.

 

[Gryz]

Are you sure this problem is caused by lack of compute-power ?

It could be memory. Suppose the program you regard with highest priority doesn't need memory for the first few minutes of execution. Suppose other programs do allocate a bunch of memory. Now your high priority program suddenly wants a lot more memory. There isn't any. So your system starts swapping pages. (RAM to page-file on the CPU, or VRAM to RAM on a GPU). That will cause relatively big slow-downs.

How would you want to prevent this ? Disallow the lower-prio programs to allocate memory ? That'll be hard to do. And it might be a waste of resources, if you don't know there is (or will be) a higher prio program needing more memory later.

Problems can be even more complex. You might have enough cpu-power and enough memory. But if you need a lot of communication between different components, that might be the bottle-neck. CPU to RAM. CPU to GPU. CPU to VRAM. Audio. Network-interface. RAM to HDD. If there is enough data being pumped around, caches will become useless. Busses will be full, and programs will have to wait. Sometimes two or three consumers of a particular resource will cause trashing.

The average user sees something slower than usual. "Oh, my computer is slow". But in reality they have no idea what it is, that is making it slow. Technology is often more complex than you think at first. And very few people will actually go into the details to find out exactly what is wrong.

 

[tweakboy]

Nice response