Turbo Core Finds Its Way Into APUs
Whereas AMD launched Llano with a limited number of SKUs, none of which were unlocked or equipped with Turbo Core functionality, all six of the Trinity-based APUs currently being discussed are equipped with Turbo Core, and three of them are unlocked.
Of course, because an APU contains x86 and graphics compute units, managing performance against thermal output requires communication between all of the chip's functional components. Each Piledriver module has its own power monitor, which reports to a manager in the on-die northbridge. The monitors keep tabs on power consumption in a deterministic fashion, based on the module’s activity. The GPU has a power monitor of its own, which also measures power use based on each compute unit’s activity.
Using data from those three monitors (on the four-core APUs), the northbridge integrates power over time. When consumption is less than TDP, active resources are able to run faster up to the available power headroom. As with FX, Turbo Core supports two levels of boosted P-states, which can be used to increase CPU frequency by any number of 100 MHz increments.
The behavior of Turbo Core is now being referred to as bi-directional, since data from multiple sources must be read as input before output (frequency control) can be applied. As a result, the APU operates at different clock rates depending on whether the workload is lightly threaded, heavily threaded, or GPU-intensive.
It’s easiest to measure the effect of Turbo Core in a lightly-threaded application that leaves the most thermal headroom on the table. A run through our same iTunes conversion shows a 4% speed-up attributable to AMD’s third-gen Turbo Core technology.
Of course, there are going to be enthusiasts who, rather than allow Turbo Core to push performance modestly, wish to get more aggressive on their own.
AMD recognizes this, giving its K-series parts unlocked multiplier ratios for easier access to higher clock rates without affecting the frequency (and consequently, the stability) of other on-board subsystems. Because these APUs incorporate a graphics engine as well, though, that component's performance is also adjustable.
Despite the early status of our FM2-equipped motherboards, we managed to crank our A10-5800K up to 4.5 GHz using core voltage settings as high as 1.5 V. Windows would start to boot at 4.6 and 4.7 GHz, but never made it to the desktop before locking up. AMD says that, using a different platform, it's able to hit 4.8 GHz on air cooling. As we get closer to channel availability, we have to guess that platform vendors will better-optimize the overclocking headroom of K-series SKUs, particularly since there will be three of them at launch.
AMD also makes it a point to note that overclocking its x86 cores is far less effective than tuning the graphics engine. And while the Radeon HD 7660D on our -A10-5800K is set to operate at 800 MHz by default, it's running beyond 1 GHz in AMD's lab. Unfortunately, while our ASRock-based platform has a field for graphics overclocking, setting it higher currently doesn't seem to affect performance. We'll need to revisit overclocking later this year.