5870 Bottleneck Investigation (CPU and/or Memory Bandwidth)

[Lightman]

Bench a video game at different ram frequencies 800mhz - 1400mhz

I came close CCC limits 900-1300MHz for mem

All tests done @1920x1200













Enjoy!

[hurleybird]

Well, from the initial results it looks like HD 5870 responds to more memory bandwidth, but 100MHz mem OC doesen't tell us much. For all we know 150 more MHz on the memory would stop scaling. What we want to know is the point where overclocking the the memory stops giving more performance, as well as the point where overclocking core stops giving more performance. Here's a better methodology:

1. Download AMD GPU clock tool for HD 5870

2. Underclock both core and memory to half frequency (425/600) to keep the same Compute/bandwidth ratio.

3. Test at that frequency

4. While keeping the core @ 425MHz, start increasing the memory clock by some increment, say 50-100MHz, until it stops scaling or becomes unstable.

5. While keeping the memory @ 600MHz, start increasing the core clock by some increment, say 50-100MHz*, until it stops scaling or becomes unstable.

6. Repeat with as many programs as you care for.

7. Analyze

*Might be easier to have the same % increment as for memory. For example, if you use 100MHz increments on both, each increment is more substantial for compute resources because it starts at a lower frequency (450 vs. 600MHz.) If you want to have proper proportions, a 100MHz increase on mem has the same significance as a ~71MHz (70.833) increase in compute. In other words, multiply whatever you choose as the memory increment by 0.70833 to get the amount you should increment core by.