Gaming Performance (Discrete GPU)

For our gaming tests, we are using our AMD Ryzen 9 5950X paired with an NVIDIA RTX 2080 Ti graphics card. Our standard test suite consists of 12 titles, tested at four configurations:

  • Stage 1: Actual Gaming (1080p Maximum Quality, or equivalent)
  • Stage 2: All About Pixels (‘4K Minimum’ Quality)
  • Stage 3: Medium Low (‘1440p Minimum’)
  • Stage 4: Lowest Lows (720p Minimum or lower)

The final three settings are a set of CPU-limited gaming, and help find the limit of where we move from CPU limited to GPU limited. Some users baulk at this testing finding it irrelevant, however these configurations have been widely requested over the years. The contraire to this testing is the first setting, at 1080p Maximum: this being requested given that 1080p is the most popular gaming resolution, and Maximum Quality because this graphics card should be able to handle almost everything at that resolution at very playable framerates.

All the details for our gaming tests can be found in our #CPUOverload article.

Stage 1: Actual Gaming
AMD Ryzen 9 5950X, SMT On vs SMT Off
AnandTech Settings Average
Chernobylite 1080p Max 100% -
Civilization 6 1080p Max 103% -
Deus Ex: MD 1080p Max 99% 100%
Final Fantasy 14 1080p Max 102% -
Final Fantasy 15 8K Standard 100% 99%
World of Tanks 1080p Max 100% 102%
World of Tanks 4K Max 103% 102%
Borderlands 3 1080p Max 101% 103%
F1 2019 1080p Ultra 103% 106%
Far Cry 5 1080p Ultra 104% 104%
GTA V 1080p Max 99% 100%
RDR 2 1080p Max 100% 100%
Strange Brigate 1080p Ultra 101% 101%

In real-world gaming situations, there’s very little to pick between having SMT enabled or disabled. Almost universally it is either beneficial or a smidgen better to have it enabled, with F1 2019, Civilization 6, and Far Cry 5 seemingly the best recipients. I’ve also added in the Stage 3 result from World of Tanks, just because that benchmark doesn’t really have a proper settings menu.

Stage 2: All About Pixels
AMD Ryzen 9 5950X, SMT On vs SMT Off
AnandTech Settings Average
Chernobylite 4K Low 99% -
Civilization 6 4K Min 105% -
Deus Ex: MD 4K Min 98% 100%
Final Fantasy 14 4K Min 102% -
Final Fantasy 15 4K Standard 100% 100%
Borderlands 3 4K Very Low 101% 104%
F1 2019 4K Ultra Low 100% 100%
Far Cry 5 4K Low 101% 100%
GTA V 4K Low 100% 101%
RDR 2 8K Min 100% 100%
Strange Brigate 4K Low 100% 100%

With our high resolution settings with minimal quality, there is only one outlier in Civilization 6 on the average frame rates, which seem to be a bit higher when SMT is enabled.

Stage 3: Medium Low
AMD Ryzen 9 5950X, SMT On vs SMT Off
AnandTech Settings Average
Chernobylite 1440p Low 100% -
Civilization 6 1440p Min 105% -
Deus Ex: MD 1440p Min 97% 96%
Final Fantasy 14 1440p Min 102% -
Final Fantasy 15 1080p Standard 101% 105%
World of Tanks 1080p Standard 101% 101%
Borderlands 3 1440p Very Low 103% 105%
F1 2019 1440p Ultra Low 99% 99%
Far Cry 5 1440p Low 99% 99%
GTA V 1440p Low 100% 99%
RDR 2 1440p Low 100% 100%
Strange Brigate 1440p Low 100% 100%

At the more medium settings, we’re starting to see some more variation (Borderlands gets a few percent from SMT). We’re starting to see Deus Ex:MD drop off a bit with SMT enabled.

Stage 4: Lowest Lows
AMD Ryzen 9 5950X, SMT On vs SMT Off
AnandTech Settings Average
Chernobylite 360p Low 106% -
Civilization 6 480p Min 102% -
Deus Ex: MD 600p Min 91% 91%
Final Fantasy 14 768p Min 102% -
Final Fantasy 15 720p Standard 99% 102%
World of Tanks 768p Min 101% 100%
Borderlands 3 360p Very Low 108% 110%
F1 2019 768p Ultra Low 102% 105%
Far Cry 5 720p Low 100% 101%
GTA V 720p Low 99% 98%
RDR 2 384p Low 100% 103%
Strange Brigate 720p Low 95% 95%

This is perhaps our most varied set of results, with Deus Ex:MD showing an almost 10% drop with SMT enabled. DEMD is usually considered a CPU title, but so is Chernobylite, which sees a 6% gain. Borderlands is +8-10% with SMT enabled, which is more of a modern game. However, I doubt anyone is playing at these resolutions.

Overall Gaming Performance

If we take full averages from all the data points, then we’re seeing a rough +1% gain in performance in the more complex scenarios across the board.

Resolution Average Comparison
AMD Ryzen 9 5950X, SMT On vs SMT Off
AnandTech Setting aka Average
Stage 1 1080p Max Actual Gaming 101% 101%
Stage 2 4K+ Min All About Pixels 101% 101%
Stage 3 1440p Min Medium Lows 101% 101%
Stage 4 < 768p Min Lowest Lows 100% 101%

In reality, any loss or gain is highly dependent on the title in question, and can swing from one side of the line to the other. It’s clear that Deus Ex prefers SMT off, and F1 2019 or Borderlands prefers SMT on, but we are talking fine margins here.

CPU Performance Power Consumption, Temperature
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  • Machinus - Thursday, December 3, 2020 - link

    Can you sell me yours so I can try one?
  • Marwin - Thursday, December 3, 2020 - link

    For me the main question is not whether SMT is bad or good in multithread, but how it is good or bad for 2-4-6 thread loads on for example 12 core Ryzen. When windows may or may not schedule threads to real cores (by 1 thread of 1 core) or to SMT cores in series
  • Duraz0rz - Thursday, December 3, 2020 - link

    IIRC, Windows knows what cores are real vs virtual and what virtual core maps to a real core. It shouldn't matter if a thread is scheduled on a real or virtual cores, though. If a thread is scheduled on a virtual core that maps to a real core that's not utilized, it still has access to the resources of the full core.

    SMT doesn't come into play until you need more threads than cores.
  • GreenReaper - Thursday, December 3, 2020 - link

    That's not *quite* true. Some elements are staticly partitioned, notably some instruction/data queues. See 20.19 Simultaneous multithreading in
    "The queueing of µops is equally distributed between the two threads so that each thread gets half or the maximum throughput."

    This partitioning is set on boot. So, where each thread might get 128 queued micro-ops with SMT off, you only get 64 with it on. This might have little or no impact, but it depends on the code.

    The article itself says: "In the case of Zen3, only three structures are still statically partitioned: the store queue, the retire queue, and the micro-op queue. This is the same as Zen2."
  • jeisom - Thursday, December 3, 2020 - link

    Honestly it looks like you provided a 3rd viewpoint. As these are general purpose processors it really depends on the workload/code optimization and how they are optimized for a given targeted workload.
  • jospoortvliet - Thursday, December 3, 2020 - link

    Hmmm, if you have a *very* specific workload, yes, 'it depends', but we're really talking HPC here. Pretty much nothing you do at home makes it worth rebooting-and-disabling-SMT for on an AMD Zen 3.
  • Holliday75 - Thursday, December 3, 2020 - link

    The confusion comes in because these are consumer processors. These are not technically HPC. Lines are being blurred as these things make $10k CPU's from 5-10 years ago look like trash in a lot of work loads.
  • GeoffreyA - Thursday, December 3, 2020 - link

    Interesting article. Thank you. Would be nice to see the Intel side of the picture.
  • idealego - Thursday, December 3, 2020 - link

    I imagine compiler optimization these days is tuned for SMT. Perhaps this could have been discussed in the article? I wonder how much of a difference this makes to SMT on/off.
  • bwj - Thursday, December 3, 2020 - link

    This article ignores the important viewpoint from the server side. If I have several independent, orthogonal workloads scheduled on a computer I can greatly benefit from SMT. For example if one workload is a pointer-chasing database search type of thing, and one workload is compressing videos, they are not going to contend for backend CPU resources at all, and the benefit from SMT will approach +100%, i.e. it will work perfectly and transparently. That's the way you exploit SMT in the datacenter, by scheduling orthogonal non-interfering workloads on sibling threads.

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