By now, many know that every AMD Ryzen™ processor offers a suite of capabilities called AMD SenseMI technology. This suite of intelligent features allows our processors to understand their operating environment and adapt for lower power consumption, better performance, and cooler operation.1

 

One of the key performance technologies in AMD SenseMI is called Precision Boost. Precision Boost allows an AMD Ryzen processor to dramatically increase clockspeeds when the CPU has electrical, thermal, and/or utilization headroom to spare. In other words: if the processor’s analysis of its own environment indicates that it can safely go faster… it will! Precision Boost is a core capability of AMD Ryzen processors for desktop PCs, which we launched in March of this year.

 

 

More recently, we introduced a new relative in the Ryzen family: the AMD Ryzen Mobile Processor with Radeon™ Vega Graphics for ultrathin laptops. The nimble and efficient Ryzen Processors with Radeon Graphics have an evolved version of Precision Boost with a straightforward name: Precision Boost 2. Today we’ll be looking at how Precision Boost and Precision Boost 2 compare, and show how the enhanced capabilities of Precision Boost 2 can capitalize on new performance opportunities.

 

Boost Basics

Besides the specifications you can read on the side of the box, processors also have specifications that define safe operating temperatures and power draw from your motherboard. Of course, different programs will also use a certain percentage of the CPU’s circuits. It is useful to imagine these three limits —power, temperature, and utilization—as a triangle. For the sake of conversation, let’s call that the “reliability triangle.” To ensure your processor is reliable over the long haul, it makes sense that processors self-manage to stay inside the reliability triangle.

 

Precision Boost

But if the processor isn’t likely to leave the reliability triangle when processing a given workload, then that processor should also be able to recognize the opportunity to go faster for more performance. That’s where Precision Boost steps in! Precision Boost can continuously raise clockspeeds until reaching the rated maximum frequency, or reaching a boundary of the triangle (whichever comes first). Once the clockspeed reaches one of these limits, Precision Boost will try to maintain that peak performance by tweaking the clockspeed up and down in small increments of just 25MHz.

 

Precision Boost on the AMD Ryzen desktop processor uses the above behavior in two modes: when an application is using up to two CPU cores (“two-core boost”), or more than two CPU cores (“all-core boost”). The maximum clockspeed for the two-core boost is higher, because fewer cores predictably use less energy and generate less heat. This bimodal boost configuration is a great way to ensure relatively consistent or predictable boost behavior as workloads change.

 

The AMD Ryzen™ 5 1600 processor provides a helpful real-world example:

  • It can boost up to 3.6GHz for workloads using 1-2 cores
  • It can boost up to 3.4GHz for workloads using 3-6 cores
  • And it has a base clock of up to 3.2GHz if boost is not feasible

 

Precision Boost 2

Precision Boost 2 for the Ryzen Processor with Radeon Graphics is also based on the reliability triangle, but with a major difference: Precision Boost 2 does not impose a lower clock speed limit if more than two CPU cores are being used. Precision Boost 2 only assesses whether the processor is within specifications, and continues to boost—on any number of cores—until reaching the maximum clockspeed printed on the box, or bumping into a boundary on the reliability triangle (whichever comes first).

 

This new, more flexible boost can have a big impact on applications that spawn many lightweight processing threads. Even collectively, light threads often don’t demand much of the processor, which means they don’t require much energy or generate much heat to process. Where an AMD Ryzen desktop processor with Precision Boost would move into the lower frequency all-core boost for such workloads, Precision Boost 2 can allow a Ryzen Mobile Processor with Radeon Graphics to keep cranking the clockspeeds as high as possible on however many cores the workload requires.

 

If you were to chart the CPU clockspeeds in a workload from one to many threads, the plot you could draw for Precision Boost 2 is more graceful and gradual than its predecessor with increased numbers of active cores. And for workloads with many cores in use, Precision Boost 2 can be especially opportunistic about capitalizing on headroom opportunities (Figure 1).

 


Figure 1: Precision Boost 2 enables new opportunities to raise CPU frequencies on Ryzen Processors with Radeon Vega graphics, (Red) especially when there are many threads in flight. Chart for illustrative purposes.

 

 

But a scenario you can measure is even better! To do that, we fired up an application called OCCT. OCCT is a stability tester that scales nicely from one to many threads. That scalability is a perfect way to show you how Precision Boost 2 has a graceful and opportunistic behavior as more cores become used.

 

In figure 2, we’re looking at OCCT on the AMD Ryzen™ 7 2700U processor This is a four core, eight thread processor with a base clockspeed of 2.2GHz and a boost frequency of up to 3.8GHz. At the left end of the chart, we see a single worker thread hit close to the max at 3.67GHz, and gradually level off to about 2.9GHz as more cores and threads were used.

 

  

Figure 2: Precision Boost 2 running on 1-8 CPU threads in the 4C8T AMD Ryzen 7 2700U. Precision Boost 2 enables notable clockspeed upside, even with the maximum number of threads. Tested as of 10/27/2017 by AMD performance labs in the HP ENVY x360 notebook: 2x4GB DDR4-2400, Samsung 850 EVO SSD, 1080p display, Windows® 10 x64 1703, AMD Ryzen™ 7 2700U, graphics driver 17.11.

 

This graceful curve illustrates the environmental awareness of Precision Boost 2, but take note of the 2.9 GHz frequency on the right end of the chart: it’s a full 700MHz above the base clockspeed on all threads. It’s proof positive that Precision Boost 2 can intelligently enable big CPU frequency increases on any number of active threads!

 

Being an opportunistic boost algorithm, however, it’s important to point out that the exact behavior of Precision Boost 2 will vary with the workload and the system. As a general set of guidelines: Lighter apps get more boost, heavier apps get less boost. Cooler temperatures get more boost, warmer temperatures get less boost. But, overall, Precision Boost 2 in the Ryzen Processor with Radeon Graphics is designed to let more cores boost more often for more performance in your PC.

 

If you’re interested in learning more about the processors with Precision Boost 2, check out the AMD Ryzen Processor with Radeon Vega graphics, which we just launched for ultrathin notebook PCs.

 

Robert Hallock is a technical marketing guy for AMD's CPU division. His postings are his own opinions and may not represent AMD’s positions, strategies or opinions. Links to third party sites are provided for convenience and unless explicitly stated, AMD is not responsible for the contents of such linked sites and no endorsement is implied.

 

Footnotes:

  1. Visit amd.com/en/technologies/sense-mi for complete details of the AMD SenseMI technologies and per-processor capabilities.