Discussion 3900X SMT ON or OFF for current games


Dec 6, 2018
The reasoning is the following if 6 cores 12 threads is the sweatspot in current games and 8C16T isn't bringing that much on the table then the question you can ask is: if 12T is what current games like what if I give each thread its own core.

Advantage: (if the game really only uses 12 threads)
- Cache isn't punched out by the other thread, so act a bit like it has more (game)cache.
- The threads don't hinder each other that much.

- If the game likes more than 12 threads it may slow down when going from 24 to 12. I assume if off is better now in the (far) future more games may like it on to beat an 8C16T
- 12C12T uses more power than 6C12T (but since 9900K we don't care ;) ) but it most likely uses less power per core than the 6C12T

Yeah I see you thinking what does that mean for 3950X 16 cores for games...

Note that setting SMT to off on an 6C12T to 6C6T will probably cost you if the game likes more than 6 threads. (most games I would think)

There is a video out there that doesn't mean much (and could be manipulated) since it compares the 3900X with another system instead of SMT on vs SMT off of the same system (we are waiting for those test)
Compared to 9900K stock, but who uses 9900K stock?
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Golden Member
Nov 22, 2016
Compared to 9900K stock, but who uses 9900K stock?
>99% of 9900K owners I would suspect.

Overclockers need to realise that they are a niche of a niche (high performance CPU segment is small in itself). While it may be uncomfortable to them in their little geek-bubble; most of the world does not have the same mindset as them (thankfully).


Dec 6, 2018
We didn't have to wait long for that review :)

Looks interesting so it looks like in games it behaves like +200Mhz or -200Mhz I would guess, so you should know which game you play when you really want this extra 4% out of it.

So how easy can it be switched on or off like in a game profile?

P.S. when you are also streaming this will obviously not look as good, you may even end up below 9900k level speed. (depending on stream settings)
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Senior member
Jun 13, 2013
- Cache isn't punched out by the other thread, so act a bit like it has more (game)cache.
On Intel this is always true, since all L3 cache is shared by all cores. On AMD You can arrive to this situation: some game threads share important state and stay inside CCX, 3Cores/6Threads "fit" the workload, after disabling HT now some threads do not fit 3Cores and have to communicate through memory.
So there is less contention for L3 Cache, but also there is less slots for "home threads". And in games almost everything is shared, game state between threads, render thread output is fed into GPU drivers etc.


Junior Member
Jul 20, 2019
Hardware Unboxed also covered this:

Conclusion is...
maybe, a little, but unless gaming in certain titles is all you do then it's probably not worth it.

EDIT: and just realised that Reddit article referenced the same video.