Overclocking is obviously a big part of the marketing behind Piledriver FX. In fact, it’s right there in the logo: “UNLOCKED”.
Indeed, every single FX model comes unlocked, allowing you to easily overclock the CPU and NB by simply increasing multipliers. AMD even sells a version of the CPU that comes with a closed-loop liquid cooler, and it’s a heavy duty one at that.
The liquid cooler is the same model that was sold with the Bulldozer FX 8150, and if you’re familiar with Asetek built coolers (the majority of the market is comprised of either rebranded Asetek products, or copied products resulting in lawsuits), you know what to expect. This particular kit from AMD is designed for 120mm fans, and is very thick at 50mm. The two included fans ramp up to a very fast (and LOUD) 2200 RPM.
The solution is obviously not as ‘extreme’ as a custom water cooling kit, but for something that is just about as easy to install as a standard heatsink, it’s pretty good. We will use it to test overclocking, along with a Phanteks PH-TC14PE to represent high end air cooling.
Please note that this method of overclocking is meant to find the highest clock speeds, not necessarily the best performance. In other words, it would be better to take the time to increase HT speeds once the high clock speed is found. I am going to stop short of that, unless it is to pinpoint an exact fail point.
With the liquid cooler installed, overclocking began. I usually take a very procedural approach to overclocking, increasing clock speeds and voltages step by step. But this time I went straight for 5 GHz. With the voltage set to 1.45v, and the LLC set to “Extreme” it booted up into Windows fine! I was able to snag a screenshot in CPU-Z before continuing to stress testing. Unfortunately, stress tests would cause failures pretty much immediately each time. I tried ramping up the voltage, going as far as 1.6v before giving up on the lofty 5 GHz goal. It is painful to see it right there in my grasp, but if it fails under load, what’s the point?
The next step was 4.9 GHz at 1.5v, and it seemed to have no problems with 10 minutes of load testing (LinPack with AVX). From there, I sought out the lowest voltage it would remain stable at, and got it down to 1.455v. With LLC still set to Extreme, the voltage would still jump to 1.5v under load, which is probably why it was so stable.
After an hour of LinPack, I got to work on the NB. Using multipliers, the frequencies go up in 200 MHz increments, so this can be difficult to pinpoint. With a NB voltage as high as 1.45v, it would not boot with a NB higher than 2600 MHz. Increasing HT reference (and lowering other multipliers) was of no use either, so it seems that this particular chip is limited to a 2600 MHz NB.
After that came our stability test of an overnight LinPack run. Everything checked out there, so I called it: 4.9 GHz at 1.45v
Next I sought out how high the FX 8350 would go underneath the Phanteks cooler. Set up in dual-fan mode running at full speed, this cooler is still extremely quiet. It’s not as silent as a Noctua NH-D14, but performs great under load.
After hours of testing, I was constantly having problems with the CPU speed throttling to 3.4 GHz after 10-15 minutes under load. Like Bulldozer, Piledriver seems to have a certain temperature thresholed at which it simply struggles to run at full speed for very long. The liquid cooler had no problem keeping it under 60 Celsius at its stable speed. I guess when you try cramming more than 1.4 volts at near 5 GHz into a chip with 1.2 billion transistors, you are pretty much already at the limit.
Still, 4.6 GHz on air is nothing to sneeze at, and in fact is higher than I ever had Bulldozer running stable using the same liquid cooler.
Before moving on, let’s find out what our overclocking results did for us:
Our liquid based overclock resulted in a huge jump up to 8.4 in CineBench. This is well past what a Core i7 3770K does at stock speed, but not quite as much as the $1000 3960X. On air, we managed almost an 8.0, which is also pretty impressive.
Here’s another result, one with more real-world implications:
Unfortunately, overclocking has the nasty side effect of drawing even more power. Bulldozer was infamous for eating gobs of power once it hit a certain threshold. We were careful not to push Piledriver too far, but power consumption still went up:
We’re getting pretty close to 400W, but if you are running a CPU at this speed, you won’t care.
I should note now that the Gigabyte 990FXA-UD3 is not exactly a powerhouse of an overclocking board. While overclocking, Controller Hub temperatures can reach upwards of 80 degrees Celsius when not actively cooled. The voltage regulation circuit also got extremely hot under load, and seems to have a shut down point of 100 degrees. We witnessed this exact same thing with other lower-end boards. The fact is, if you plan on overclocking an AMD CPU, you really should seek out a motherboard with high end voltage regulation circuitry and cooling. We always pay specific attention to this in our motherboard reviews, so keep us in mind when looking for the right motherboard to use. I’ll try overclocking Piledriver FX again once we get a more robust board.