Introduction

If you've read our AMD Ryzen 5000 Series "Zen 3" reviews last week, you will have definitely wondered about our gaming performance scores—so did we. While application performance showed the expected impressive gains, gaming saw the new Ryzens neck and neck with Intel only. AMD marketing materials, on the other hand, show a double-digit FPS lead, which is corroborated by most reviewers, too. This lack of a clear win caused many of you to send feedback. Thanks, I always appreciate learning how people feel. Some emails weren't so nice, but still, thanks for voicing your opinion.

As promised, I spent the last few days digging into these performance numbers and found something worth reporting.

The Investigation

In order to research this more efficiently and rule out many random effects, I crafted a game in Unreal Engine 4. Similar to my graphics card apples-to-apples heatsink testing, this custom load lets me adjust each frame's render complexity dynamically without it affecting any other parameters. The game renders the same frame every time. To create a constant load that does not change over time, as we're looking for small differences here, there is no movement of any sort.

Let me explain the charts below. On the vertical y-axis, I've plotted the achieved frames per second; obviously, higher is better. There is no FPS cap, and V-Sync is off, so the system will render as fast as it can. Unreal Engine is set to render with DirectX 12. On the horizontal x-axis, a loading factor in percent is listed. This is somewhat arbitrary, think of it as "to the left, each frame is easier to render, so higher FPS are achieved; to the right, each frame is more complex, which puts more load on the GPU." The idea here is to be able to play with the CPU-GPU bottleneck to see at which point it occurs, and what happens.


Above, you see results for the GeForce RTX 2080 Ti used in our processor reviews. Note how AMD is posting MUCH higher FPS than Intel on the left—around 20% better. This is the Zen 3 microarchitecture IPC advantage, and it is very impressive. In this CPU-limited scenario, there is no doubt AMD is the clear winner. Actually, even the left-most point is not "100%" CPU limited because the GPU is still doing a tiny bit of work, the correct way to interpret this would be "almost completely CPU limited."

As we move to the right on the chart, we see FPS go down, which is expected behavior since the GPU gets busier and busier, which slows things down. Interestingly, the drops are almost symmetrical on both Intel and AMD, at vastly different FPS rates. Only above 40% does the gap between both platforms start to shrink.

At 80%, both AMD and Intel deliver nearly the same FPS rates—we're starting to get more and more GPU limited. Just like "CPU limited" is not a "true/false" value, "GPU limited" is more of a range as well. As GPU load increases, the CPU is left less work because there are fewer frames to perform calculations for. For graphics-related game logic, there is no reason to update states more than once per frame because you can only display updates once per frame. This lowers the CPU usage of the render thread. Other parts of the game logic, like AI, physics, and networking, run at different tick rates, usually a constant rate independent of FPS, so their CPU load is constant throughout this whole test.

Now, as GPU load increases, we gradually see a small window between 80% and 120% where the Intel "Comet Lake" platform does indeed run at higher FPS than Zen 3. I marked it with a red arrow for you. This is quite surprising, but the data is too clear to make it a random event. One theory I have is that AMD's aggressive idle-state logic shuts down some cores because they are no longer at full load. With Zen 3, they are able to do that very rapidly and without OS interaction (for power management), and spin them up just as quickly, although not instantly. I'll dig into this some more.

Once we move past 140% in the chart above, the FPS rates are pretty much identical. Is anyone surprised? The GPU is limiting the FPS here, which is typically referred to as the "GPU bottlenecking". Having now thought about this for a while, isn't it kinda obvious? Did anyone expect Zen 3 to magically increase GPU rendering performance?

Other reviews confirm this last data point, you just have to look for it in their data. Many reviewers have focused on the CPU-limited scenario, using light MOBA-style games that don't fully utilize the graphics card. This is a perfectly valid test to highlight CPU differences, of course. However, a lot of gamers are playing highly demanding AAA games, which means their GPU load is much higher and the limiting factor when it comes to FPS. Otherwise, if the graphics card is idle, even partially, money is wasted on a card that's too fast for what the rest of the system can do. This is why I believe our 1440p and 4K testing at ultra is relevant even though differences between processors are minimal in those scenarios.

Memory Speeds?

Next, I checked on the effect of memory speed. Instead of 3200 CL14, I used 3800 CL16 for this test, with the Infinity Fabric running at 1:1 IF:DRAM clock. This is the best-case scenario for AMD—my Ryzen 9 5900X can not run 2000 MHz Infinity Fabric.


Note how the shape of the curve is identical to the one with lower memory speed. There are only small differences, with the biggest takeaway here that the area where Intel is faster than AMD is still there, but much less pronounced. Interestingly, it is still in exactly the same range: 80% to 120%.