5870 Bottleneck Investigation (CPU and/or Memory Bandwidth)

[jaredpace]

Thanks lightman, wish elmore would let us know how he got his vmem up and clocked the mem at 1400mhz...
however, from your tests on the canyon flight FPS @ 850mhz core

memory mhz / FPS / fps Increase
0900 / 091.7 / 0 0%
1000 / 095.2 / +3.5 +3.8%
1100 / 097.9 / +2.7 +2.9%
1200 / 100.3 / +2.5 +2.5%
1300 / 102.4 / +2.1 +2.1%

According to this test, as the memory clock increases, gains are evident at 1200 -> 1300mhz. Even though they are diminishing as it goes higher, you are still getting benefits above the stock mem clock, which backs peoples assumptions that the card is bottlenecked @ 153gbps. Would like to see memory at 1400mhz, if it yields a ~2% increase over 1300mhz, it's even further proof.

Lightman's overall FPS is still increasing so his memory is not producing errors yet

"Overclocking the memory on these cards is quite different from any other card so far. Normally you'd expect rendering errors or crashes, but not with these cards. Thanks to the new error correction algorithm in the memory controller, every memory error is just retransmitted until everything is fine. So once you exceed the "stable" clock frequency, memory errors will appear more often, get retransmitted, but the rendered output will still look perfectly fine. The only difference is that performance drops, the further you increase the clocks, the lower the performance gets. As a result a normal "artifact scanning" approach to memory overclocking on the HD 5800 Series will not work. You have to manually increase the clocks and observe the framerate until you find the point where performance drops."
http://www.techpowerup.com/reviews/A...D_5870/33.html