Does Disabling SMT on a Ryzen 7 CPU Improves its Performance?

The performance of the new Ryzen 7 CPU from AMD has beed causing a lot of controversy: it is faster than its competitor in some tests, but it is slower in other ones, and several theories have been raised about the reason why. A popular theory says that disabling the SMT feature, the performance actually improves. Let’s test if is it true.
We published recently the Ryzen 7 1700X Review. It is a new CPU from AMD, based on a brand new architecture. We concluded that the Ryzen 7 1700X is faster that the Core i7-7700K in some tasks, but slower on other ones, including most games we tested.
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One of the possible causes of this is the fact that the Ryzen7 uses a completely new architecture, and the available programs and games are not optimized for it. Intel’s Core architecture, on the other hand, has been in market for years, and software developers know how to optimize their products for it. So, it is a matter of time to have optimizations for Ryzen CPUs.
There was also a suspect that there was a bug on Windows 10, related to the managing of 16 threads of the Ryzen 7 processor, and so you could have a performance improvement if you disable the SMT (Simultaneous Multi-Threading) feature. SMT is similar to the Intel Hyper-Threading technology, making each physical core to be recognized by the operating system as two threads (logical cores).
AMD, however, denied this bug; the company considers that Windows 10 is working correctly with Ryzen 7 CPUs.
So, we decided to test this hypotesis and see if is there peformance changes. We ran several tests with SMT enabled (16 threads) and the with SMT disabled (8 threads), and compared the result. Let’s check it on the following pages.
[nextpage title=”How We Tested”]During our benchmarking sessions, we used the configuration listed below. Between our benchmarking sessions, the only variable devicand was the SMT enabled or disabled at motherboard setup.
Hardware Configuration

Motherboard: ASRock X370 Taichi
Memory: 16 GiB DDR4-2133, two G.Skill Ripjaws V F4-2133C15D-16GVR 8 GiB memory modules configured at 2133 MHz
Boot drive: WD Blue 1,000 GiB SSD
Video Card: GeForce GTX 1080
Video Monitor: Philips 236VL
Power Supply: Corsair VS500

Operating System Configuration

Windows 10 Home 64-bit
NTFS
Video resolution: 1920 x 1080 60 Hz

Driver Versions

NVIDIA driver version: 378.49

Software Used

Error Margin
We adopted a 3% error margin. Thus, differences below 3% cannot be considered relevant. In other words, products with a performance difference below 3% should be considered as having similar performance.
[nextpage title=”PCMark 8″]
PCMark 8 is a benchmarking software that uses real-world applications to measure the computer performance. We ran three tests: Home, which includes web browsing, writing, light gaming, photo editing, and video chat tests; Creative, that includes web surfing, video editing, group video chat, video conversion, and gaming; and Work, which runs tasks such as writing documents, web browsing, spreadsheets, editing, and video chatting. Let’s see the results.

On the PCMark 8 Home benchmark, there was no difference between both configurations.

On the Creative benchmark, we also had no significant performance changes.

On the Work benchmark, again there was not change on performance.
[nextpage title=”3DMark”]

3DMark is a program with a set of several 3D benchmarks. Fire Strike runs a “heavy” DirectX 11 simulation. Sky Diver also measures DirectX 11 performance, and is aimed on average computers. The Cloud Gate benchmark measures DirectX 10 performance, and the Ice Storm Extreme measures DirectX 9 performance and is targeted to entry-level computers, so we don’t ran it.

Fire Strike ran 7% slower without SMT.

On the Sky Diver benchmark, the Ryzen 7 1700X was 8% slower with SMT disabled.

On the Cloud Gate benchmark, performance drops 20% without SMT.

[nextpage title=”Performance in programs”]

Cinebench R15

Cinebench R15 is based on the Cinema 4D software. It is very useful to measure the performance gain obtained by the presence of several processing cores while rendering heavy 3D images. Rendering is an area where a bigger number of cores helps a lot, because usually this kind of software recognize several processors (Cinebench R15, for example, can use up to 256 processing cores).
We ran the CPU benchmark, which renders a complex image using all the processing cores (real and virtual) to speed up the process. The result is given as a score.

On Cinebench R15 CPU benchmark, as expected, the system was 28% slower without SMT.

CPU-Z

On its current version, the well-known hardware identification software CPU-Z comes with a benchmarking tool, which measures CPU performance for one core and for all available cores.

On the single thread benchmark, the Ryzen 7 1700X performed similarly with and without SMT.

On the multiple thread benchmark, the CPU was 19% faster with SMT disabled.

DivX

We used the DivX converter, a tool included in the DivX package, in order to measure the encoding performance using this codec. The DivX codec is capable of recognizing and using all available cores and the SSE4 instruction set.
We converted a Full HD, six-minute long .mov video file into an .avi file, using the “HD 1080p” output profile. The results below are given in seconds, so the lower the better.

On DivX encoding, the CPU ran 6% faster with the SMT disabled.

Media Espresso

Media Espresso is a video conversion program that uses the graphics processing unit of the video engine to speed up the conversion process. We converted a 1 GiB, 1920x1080i, 23,738 kbps, .mov video file to a smaller 320×200, H.264, .MP4 file for viewing on a smartphone. The results below are given in seconds, so the lower the better.

Here the Ryzen 7 1700X was 7% faster with SMT off.

WinRAR

Another task where the CPU is very demanded is on file compacting. We ran a test compacting a folder with 8 GiB on 6.813 files to a file, using WinRAR 4.2. The graph below shows the time taken on each test.

On WinRAR, the CPU took 8% more time with SMT disabled.
[nextpage title=”Gaming Performance”]

Deus Ex: Mankind Divided

Deus Ex: Mankind Divided is an action RPG with FPS elements, launched in August 2016, that uses the Dawn engine, being compatible with DirectX 12. We tested it using the benchmark included in the game, with DirectX 12 enabled, Full HD, and graphic options as “medium”.
The results below are expressed in frames per second.

On this game, the Ryzen 7 1700X was 11% faster when we disabled SMT.

Dirt Rally

Dirt Rally is an off-road racing game released in April 2015, using Ego engine. To measure performance using this game, we ran the performance test included in the game, in 1920 x 1080 (Full HD) resolution and image quality configured as “medium” and MSAA off.
The results below are expressed in frames per second (fps).

In this game, there was no performance change disabling SMT.

Grand Theft Auto V

Grand Theft Auto V, or simply GTA V, is an open-world action game released for PCs in April of 2015, using the RAGE engine. In order to measure the performance on this game, we ran the performance test of the game, measuring the frame rate with FRAPS. We ran GTA V at Full HD, with all image quality set as “high” and MSAA off.

The results below are expressed in frames per second.

On GTA V, we also had no performance change.

Hitman

Hitman is an action/stealth game, launched in March 2016, that uses a DirectX 12 compatible version of the Glacier 2 engine. To measure performance in this game, we ran the benchmark in it, measuring the framerate with FRAPS. We ran this game with DirectX 12 enabled, with image quality set as “high”.
The results below, in Full HD and 4K, are expressed in frames per second.

Hitman ran 6% faster with SMT disabled.

Rise of the Tomb Rider

Rise of the Tomb Rider is an adventure/action game launched in January of 2016, based on Foundation engine. In order to measure the performance using this game, we ran the benchmark included on it, using Full HD resolution and graphics quality set to “medium”.
The results below are expressed in frames per second.

Also on Rise of the Tomb Rider, the computer performed the same with with SMT disabled and enabled.
[nextpage title=”Conclusions”]
After testing the Ryzen 7 1700X with SMT enabled and disabled, we can say that disabling it can improve performance in some programs. From the games we testes, Hitman and Deus Ex: Mankind Divided had a small raise of the frame rate when we configured the CPU to stay with eight threads, as well as with Media Espresso and DivX Converter.
However, in programs that use all the available threads (like Cinebench R15), there was a significant performance loss when SMT was disabled.
This means the decision of disabling SMT or not will depend on your usage: if you only want to play games, it can be a good idea to disable the feature, since none of the games we testes took advantage of it. On the other hand, if you use your computer to video or image renderization, or any application that actually uses 16 threads, it is better to keep it enabled.
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