Surprising behavior of my AMD APU on gravitational-wave GPU tasks
2 May 2020 18:04:13 UTC
Topic 222305
(moderation:
I was playing around with a Dell Inspiron 11 3185 (with an AMD A9-9420e processor)
https://www.notebookcheck.net/AMD-A9-9420e-SoC-Benchmarks-and-Specs.308002.0.html
If I tried to run even a single CPU-only task (for World Community Grid), the Einstein gravitational-wave GPU task would run three times slower. This surprised me because my processor has 2 physical CPU cores and the other core was hardly being used! I was doing this on Windows 10, and it is reproducable. The computer had be upgraded to 8 GB of RAM, and the RAM was not being maxed out.
I have read at these forums that, unlike most other GPU projects, GPU tasks at Einstein sometimes require fast memory. My *guess* is that my AMD APU doesn't allow the GPU to access the memory if the CPU is accessing memory? Any thoughts?
Thanks!
Just the nature of an APU.
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Just the nature of an APU. The cpu and gpu share memory so processes on either cpu or gpu affects the other tremendously because of trying to get access to the shared memory.
The general advice for compute is to not use both at the same time.
The other limitation on that
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The other limitation on that model of that processor is it shares 1 floating-point arithmetic unit between two physical cores. If you have 4 cores you have 2 floating-point units... etc.
This plus the memory bandwidth limits of that design is what makes it hard to be productive on both the CPU and the gpu at the same time.
Tom M
A Proud member of the O.F.A. (Old Farts Association). Be well, do good work, and keep in touch.® (Garrison Keillor) I want some more patience. RIGHT NOW!
Shared FPU (and memory)!
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Shared FPU (and memory)! Brilliant!