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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  • abufrejoval - Thursday, December 3, 2020 - link

    It's hard to imagine a transistor defect that would break *only* SMT. As you say all non-SMT chips are really SMT chips internally and the decision to disable SMT doesn't really result in huge chunks of transistors going dark (the potential target area for physical defects).

    I'd say most of the SMT vs. no-SMT decisions on individual CPUs are binning related: SMT can create significantly more heat because there is less idle which allows the chip to cool. So if you have a chip with higher resistance in critical vias and require higher voltage to function, you need to sacrifice clocks, TDP or utilization (and permutations).
  • leexgx - Saturday, December 5, 2020 - link

    With HT off I have definitely noticed less smoothness windows, as with HT it can keep the cpu active when a thread is slightly stuck
  • iranterres - Thursday, December 3, 2020 - link

    Why are people still testing SMT in 2020? Cache coherency and hierarchy design is mature enough to offset the possible instruction bottleneck issues. I don't even know the purpose of this article at all... Anyways, perhaps fallng back to 2008? Come on...
  • quadibloc - Friday, December 4, 2020 - link

    Well, instead of testing the concept of SMT, which has been around for a while, perhaps one could think of it as testing the implementation of SMT found on the chips we can get in 2020.
  • eastcoast_pete - Friday, December 4, 2020 - link

    Thanks Ian! I always thought of SMT as a way of using whatever compute capacity a core has, but isn't being used in the moment. Hence it's efficient if many tasks need doing that each don't take a full core most of the time. However, that hits a snag if the cores get really busy. Hence (for desktop or laptop), 6 or 8 real cores are usually better than 4 cores that pretend to be 8.
  • AntonErtl - Friday, December 4, 2020 - link

    I found the "Is SMT an good thing" discussion (and later discussion of the same topics) strange, because it seemed to take the POV of someone who wants to optimize some efficiency or utilization metric of someone who can choose the number of resources in the core. If you are in that situation, then the take of the EV8 designers was: we build a wide machine so that single-threaded applications can run fast, even though we know the wideness leads to low utilization; we also add SMT so that multi-threaded applications can increase utilization. Now, 20 years later, such wide cores become reality, although interestingly Apple and ARM do not add SMT.

    Anyway, buyers and users of off-the-shelf CPUs are not in that situation, and for them the questions are: For buyers: How much benefit does the SMT capabilty provide, and is it worth the extra money? For users: Does disabling SMT on this SMT-capable CPU increase the performance or the efficiency?

    The article shows that the answers to these questions depend on the application (although for the Zen3 CPUs available now the buyer's question does not pose itself).

    It would be interesting to see whether the wider Zen3 design gives significantly better SMT performance than Zen or Zen2 (and maybe also a comparison with Intel), but that would require also testing these CPUs.

    I did not find it surprising that the 5950X runs into the power limit with and without SMT. The resulting clock rates are mentioned in the text, but might be more interesting graphically than the temperature. What might also be interesting is the power consumed at the same clock frequency (maybe with fewer active cores and/or the clock locked at some lower clock rate).

    If SMT is so efficient (+91%) for 3DPMavx, why does the graphics only show a small difference?
  • Bensam123 - Friday, December 4, 2020 - link

    Anand, while I value your in depth articles you guys really need to drop the 95th percentile frame times and get on board with 1% and .1% lows. What disrupts gaming the most is the hiccups, not looking at a statistically smooth chart. SMT/HT effects these THE most, especially in heavily single threaded games. If you aren't testing what it influences, why test it at all? Youtube reviews are also having problems with tests that don't reflect real world scenarios as well. Sometimes it's a lot more disagreeable then others.

    Completely invalid testing methodology at this point.

    My advice based on my own testing. You turn off SMT/HT except in scenarios in which you become CPU bound, across all cores, not one. This improved .1 and 1% frame time... IE stutters. You turn it on when you reach a point of 90%+ utilization as it helps and a lot when your CPU is maxed out. Generally speaking <6 and soon to be 8 cores should always have it on.

    You didn't even test where this helps the most and that's low end CPUs vs high end CPUs where you find the Windows scheduler messes things up.

    Also if you're testing this on your own, always turn it off in the bios. If you use something like process lasso or manually change affinity, windows will still put protected services and process onto those extra virtual cores causing contention issues that lead to the stuttering.

    Most obvious games that get a benefit from SMT/HT off are heavily single threaded games, such as MOBAS.
  • Gloryholle - Friday, December 4, 2020 - link

    Testing Zen3 with 3200CL16?
  • peevee - Friday, December 4, 2020 - link

    "Most modern processors, when in SMT-enabled mode, if they are running a single instruction stream, will operate as if in SMT-off mode and have full access to resources."

    Which would have access to the whole microinstruction cache (L0I) in SMT mode?
  • Arbie - Friday, December 4, 2020 - link

    Another excellent AT article, which happens to hit my level of knowledge and interest; thanks!

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