Precision Boost Overdrive - A NEW Way To Overclock?
Precision Boost Overdrive - Details & Benchmarks
The road to a stable overclock is often paved with the tears of failed attempts, hours of frustration and the loss of some key features. A great example of this can be seen with Intel’s newest Skylake-X HEDT parts which have the capability to reach impressive frequencies through overclocking but to achieve the highest possible clock speed, many essential power saving and efficiency-focused elements have to be disabled. The result is often extreme current requirements and heat production. On AMD Theradripper systems, getting those higher speeds means disabling SenseMi elements like Precision Boost.
While AMD still allows for manual overclocking of Threadripper 2 processors, they’ve instituted a “middle ground” between manual overclocking and stock settings. Called Precision Boost Overdrive (PBO), it still allows for higher performance but does so without sacrificing Precision Boost 2 and XFR 2.
PBO basically takes the limits dictated by Precision Boost 2 for package power, thermal design current and electrical design current and increases them by a preset amount. This means the Precision Boost curve you saw earlier in this review moves upwards in a dynamic fashion so all cores can achieve higher clocks. The result can be up to a 13% jump in multi threaded throughput of more depending on how far you push this setting.
All of this sounds great on paper but before I get too much further into this section, there needs to be a mention about warranty. Since PBO effectively allows the CPU to run beyond its design parameters, engaging it will void your warranty. So take everything that follows with a word of warning: even though Precision Boost Overdrive is easy to enable, only you can determine if the benefits are really worthwhile.
In order to enable PBO, simply open up AMD’s Ryzen Master software suite and switch the Control Mode button from Auto to Precision Boost Overdrive. You’ll be prompted to accept a voided warranty (yes, AMD supposedly has ways to log these things within the processor) and then if its your wish, higher performance should be right at your fingertips.
After that, you’ll need to modify the three values directly below the Auto / PBO / Manual switch. These allow you to increase the following values (taken from AMD’s review guide):
Package Power Tracking (“PPT”):The PPT threshold is the allowed socket power consumption permitted across the voltage rails supplying the socket. Applications with high thread counts, and “heavy” threads, can encounter PPT limits that can be alleviated with a raised PPT limit.
Thermal Design Current (“TDC”):The maximum current that can be delivered by a specific motherboard’s voltage regulator configuration after warming to a steady-state condition through continuous operation.
Electrical Design Current (“EDC”):The maximum current that can be delivered by a specific motherboard’s voltage regulator configuration in a peak (“spike”) condition for a short period of time.
Each of these values will need to be individually modified in order for Performance Boost Overdrive to further boost clock frequencies. Now according to AMD, each motherboard manufacturer will have upper limits in place which are detected by Ryzen Master so folks can’t go absolutely nuts with these settings. However, in my experience with the Zenith Extreme, there weren’t any evident caps in place.
The great thing about Ryzen Master is that it tells you exactly what’s going on at a given point. For example, I moved PPT and TDC to 220 each (defaults of 180W) while EDC was turned to 280. This represented a significant current increase and remained within the limits I figured I’d stay within. There was of course some more headroom but having the CPU package consume upwards of 220W when under full load was plenty for this demonstration.
What became evident is that the Power Package Tracking will quickly become a clock speed bottleneck long before TDC or EDC will. As you can see in the image above, at full load it became the limiting factor in overall performance.
But does this all add up to improved benchmark results? Well lets find out with a few tests run on our 2950X…..the results are certainly interesting.
Let’s start off with a simple all-tread load scenario which in this case is AIDA64’s Stress Test. Generally PBO seems to have allowed us to increase overall the all core boost state frequencies by about 5% or 150MHz according to CPU-Z. However, what you can’t see by these screenshots is the core speed rapidly fluctuates upwards and downwards around the 37.5x multiplier without PBO enabled and 39.25x with it on. Essentially this led to an average frequency speedup of about 10% over course of the 10-minute test.
Single and lightly threaded workloads also see an improvement but it is closer to 4% on average. This is likely because Precision Boost 2 was already operating close to its maximum efficiency when in stock mode due to the power, thermal and voltage headroom lower load scenarios impart upon the CPU.
Across our synthetic tests, a pattern emerged as well. The multi threaded workloads of Cinebench and WPrime allowed the 2950X to deliver noticeably improved results with PBO enabled. Meanwhile, the single threaded scenarios in each application didn’t show any benefit at all.
The same can be said about some real world programs. Premier which doesn’t tend to overly stress all 16 cores -part of its workloads are shunted towards the GPU through CUDA- sees very little improvement while Handbrake and Blender do show some minor speedups.
Finally in gaming where lightly threaded scenarios rule, PBO offers nothing in the way of additional performance. In a way this points towards how well AMD has been able to maximize their clock speeds if Threadripper is operating below its inbred limits. However, it also means that Precision Boost Overdrive will have limited uses for people who aren’t working with higher level applications that stress 8 or more cores.