Kepler: the new frontier in overclocking
Before we get into the nitty gritty, let me just quickly define some of the new terms going to be used in this psuedo-guide.Boost Clock:
Keeping it simple for the definition. Kepler is completely dynamic. Your hardware is monitored internally, and based on the readings(temperature, power, performance, etc) your GPU core clock will be boosted above its base values to a certain point. This is your boost clock.Power Target:
Power Target is a power limiter on a percentage based scale. 100% Power Target allows your card to use 100% of its TDP, which in the 680s case is 195W. Increasing the Power Target will increase the available power to your graphics card, allowing for higher overclocks and increased temperature.
*Note, just because your power target is higher doesnt mean the increased power will always be used. Like everything else with Kepler, it's dynamic based on hardware monitoring.Clock Offset:
Again, keeping it simple. This is a new slider for overclocking. If you increase your offset to +100, your clock(either memory or core, whichever you change) will be 100MHz higher than it would be previously. The offset applies to both your base AND boost clock.
That only begins to scratch the surface, but those are essentially the basics you need to understand before going any further. I'm sure most of you are at least familiar with them at this point.
For the purposes of this example, I used stock clocks(Base: 1006MHz), 132% Power Target, auto-fan, and maxed/windowed Heaven 3.0 benchmark. Let's jump right in:
A lot to look at if you're new to this, so I highlighted the main focus of this example: Temperature, and Core clock. The benchmark was only running for about 30 seconds or so at this point. My GPU is at 69'C, and my boost clock was being pushed to 1110MHz. Let's observe what happens.
The moment my temperature hits 70'C, my boost clock scales back 13MHz and drops to 1097. The dynamic hardware monitor inside Kepler recognizes my thermals rising, and scales back my boost clock. These are the basics of how the GPU works. Lets continue to observe.
My temperature increases 9'C, and my boost clock remains the same. At this point, my temperature was holding steady.. so I manually lowered my fan to have the temperatures climb.
80'C, and another 13MHz drop in my boost clock. It's not a coincidence, 13MHz is the "step" in which the GPU will scale back your clocks based on its hardware monitoring. It's also the "step" in which your clocks will be increased when they able to be. The temperature changes from 69-70'C and from 79-80'C trigger a drop in step.OBSERVE, AND APPLY THIS KNOWLEDGE1)
Throughout the above example, you may have noticed that my power % (bottom most graph) did not come anywhere close to reaching the 132% being allotted to the GPU. Meaning to run 1110MHz (this trials maximum Boost Clock), I did not need a 132% Power Target. As a matter of fact, with my card I can turn my power target down to 85% at these settings and receive the exact same boost clock.
Does this seem significant to you? It should! Remember what we learned: Increased power = increased temperatures. Increased temperatures = a throttled boost clock. If I can run 1110 MHz at 85% Power Target, why am I allowing the card to draw more power, increase the temperatures, and potentially throttle my boost? With a maxed power target I run 1110MHz until I hit 70'C, then it drops to 1097MHz. With 85% target I hit 1110MHz just the same, but maybe I never hit 70'C to throttle me down! This is why auto-maxing the Power Target is a mistake for maximum performance, and this is what you should be testing during your overclock sessions.
If you take anything away from this thread, make it this.2)
Another observation you should make is that my Boost Clock is essentially flatlined at every 'step' in the above example, holding steady until its throttled by thermals. At the same time, power % is nowhere near the 132% being allotted to the card as mentioned in observation #1. The conclusion to make from this information: My Boost Clock is being limited by Offset
power! What if I'm not satisfied with the clocks I'm currently getting, and wanted to go higher? I have more power headroom to play with, and can tweak my Clock Offset (assuming im not hitting the limits of what my GPU is capable of).
In this scenario, where you're trying to feel out increased clocks.. go ahead and leave your power target maxed temporarily. Especially if you're trying to find your max clocks. However, the thing to remember here is maxed clocks does not necessarily translate into maximum performance.
This builds on observation #1. Sure, you can hit 1300MHz with a maxed power target (random number, I didn't do the math to see if 1300 actually coincides with the 13MHz steps from 680s base clock... probably not)
. That's swell and makes for great sig material. But what happens if those settings takes you to over 80'C? You guessed it, an automatic 26MHz (2 step) drop in your Boost clock due to thermals. So yeah, you maxed out at 1300MHz.. but your favorite benchmark spends the majority of its time running at 1274MHz. Your job at this point would be to test further and see if it's possible to stablize 1287MHz (one step down playing off the random 1300) at a lower power target and keep thermals to a level where you are not throttled at all... resulting in a higher average Boost clock over time.
I hope this helped, I tried to keep it relatively short. I'll add more if anything important stands out to me in the future.