Overclocking memory reduces performance?

[Goose]

I've had my HIS 280x for a couple of days now and I have the core running at 1200mhz which im perfectly happy with. However, if I try overclocking the memory from 1500 to 1525 i actually get a Heaven score about 15 points lower which doesn't make a great deal of sense to me.

Can anyone explain why this might be?

 

[jh30uk]

If you ran it multiple times was it same as it can vary by that each time?

Anything can have its limits and before it becomes unstable and artefacts or crashes it simply will be slower.

Try a little higher and see what happens but may be you have reached and past the sweet spot.

 

[Five.Stars]

If a memory overclock is unstable then it will produce errors. The error correction, will as a result, have a negative impact on the performance of the memory.

 

[pgi947]

You should notice correction a mile off though, you will get a kind of hitch every few seconds or so while running 3d clocks.

 

[jh30uk]

I forget about GDDR5 and error correction, same story but it will not artefact or crash as soon but push it higher and it will.

On previous VRam it was more like going up a hill then on top levelled out then down other side before it would crash.

 

[Goose]

I didn't notice any artifacts or stuttering and i'd be pretty disappointed if I cant OC the memory at all, especially as its meant to be Hynix.

Here are my results so far;

1200/1500 - 1130
1200/1525 - 1117
1200/1550 - 1122

+25 over stock is worse, +50 over stock is less worse but still not as good as stock :/

 

[wazza300]

use gpu-z and set max for both vrm's they might be getting hot and throttling

my 7970 memory was pants till I ditched the cooler and added heatsinks ect then it would clock 500mhz higher on stock v

idk if setting power control slider to 20% helps with memory also

 

[bigmac121]

If a memory overclock is unstable then it will produce errors. The error correction, will as a result, have a negative impact on the performance of the memory.

Thanks for that I had the same problem with my Classy. Just couldn't firgure it out

 

[postmanfw]

Error correction...had same with my 6950s and confused me for ages too...no artifacts or crashing just lower scores.

 

[KompuKare]

Fairly sure this has to do with GDDR5 memory latencies. No big surprise there (similar applies to CPU scores and memory overclocking), but this guy, 'The Stilt', made a popular thread on the scrypt mining boards about this:
https://litecointalk.org/index.php?topic=12369.0

For example on 7970 card the VBIOS should contain timing presets for following clock regions:
<cut>
1250MHz (1126-1250MHz)
1375MHz (1251-1375MHz)
1500MHz (1376-1500MHz)
1625MHz (1501-1625MHz)
1750MHz (1626-VCO Max)

While it is possible that it is GDDR5 error correction kicking in, the BIOS 7970 cards is meant to increase the latency going from under 1500 to going above. The latency is not meant to affect most games though (scrypt mining is very sensitive to memory latency though). I wouldn't worry about it, although it is possible that you could track down one of The Stilt's modified BIOSs if Heaven benchmarking is that important to you!

 

[Goose]

Update:

After running Heaven my VRM max temps were 74 and 64 it doesnt look as though overheating is the issue.

 

[Doco]

Do you have the power slider moved up to +20% ?I had a similar issue when I first started over-clocking my 7950 - beyond a certain point my scores were actually less while overclocked than not - the issue was that the card effectively throttled itself back because it needed more power - where your are overclocking in you should see a slider for power control - bump it up to the full +20 and re-run the benchs - you should see a difference

 

[JonSmith]

This will be due to the vBIOS altering the timings. I observe this on my HD 7850. Make sure to set your clocks to the maximum per timing domain, they're something like 1250, 1375, 1500.

It is nothing to do with error correction in this case.