GTX 970 overclock: increase voltage cause core clock increasing?

[RudiSZT3]

At first, sorry for my bad english.

I have an MSI GTX 970 Gaming. Its boost clock is 1316 MHz while gaming without any oc.

If I set core clock +150 MHz and memory clock +400 MHz (without increasing voltage), then core clock will be 1466 MHz, but when gpu-using reaches 99-100%, core clock falls back to 1454 MHz. I think it's throttling, isn't it?

But! If I increase voltage with +25mV, core clock starts on 1479 (more than it could be with the +150), and when gpu-using reaches the 99-100%, core clock falls back to the "right" 1466 MHz.

What can this mean?

Is voltage increasing cause a little clock increasing?

I know that clock increasing sometimes needs some voltage increasing to not throttle. But why does core clock jump to 1479 first, and than falls back to the aimed 1466 (+150) when gpu-using reaches the top? Why don't start at 1466 and hold it constantly?

 

[rtwjunkie]

Because it is reaching either the power or temperature limit. Try monitoring with GPU-z to see which it is.

Increase those a notch or two from where they are. Try that before adding any voltage.

 

[PHaS3]

If I remember right, that happens because of the "Pref Cap Reason" VREL (I think its VREL). When the card doesn't "think" the clocks can be maintained by the current voltage it drops the clocks. Naturally, supplying more voltage will increase the clock in this case. Be careful of increasing the voltage though.

Also, as @rtwjunkie said above, make sure it isn't reaching the power or temp limit. On my 970 i put power and temp limits to max, prioritize temp limit, and it runs at a boost of 1548 constantly when gaming, and if I remember correctly I maxed the voltage increase slider too - never seen my card hotter that 73°C though, so check your temps.