By: Jukka Larja (roskakori2006.delete@this.gmail.com), November 20, 2020 9:03 am
Room: Moderated Discussions
Andrei F (andrei.delete@this.anandtech.com) on November 18, 2020 8:34 am wrote:
> Dummond D. Slow (mental.delete@this.protozoa.us) on November 18, 2020 7:48 am wrote:
>
> > I hope eventually we get some very comparable HT/noHT CPU in AnandTech benchmark for comparing,
> > in the meantime I found this https://www.anandtech.com/bench/product/2622?vs=2652
> > Skylake @ 3,8-4,2GHz 4c/4t versus 4,0-4,2 4c/8t (sadly also has more L2 cache due to Intel's segmenting).
>
> It's something in the pipeline. Generally gaming will benefit turning off SMT even.
It is very simple why gaming often benefits from turning SMT off: it's common to have one or two threads that limit to overall performance, and anything that has even a change to slow those down is bad.
Modern game engines are a bit less affected by this than older ones, but that's mostly because they can better compensate by running other stuff in parallel (e.g. if an old engine could maybe benefit from couple of threads in addition to those one or two limiting threads, maybe a modern engine can use five. Figures are an example, actual values vary).
It's also good to note that games in general aren't optimized to go as fast as they can. They are often optimized to run at most 60 FPS or as low as 30 FPS. So when e.g. multi-threading is considered, it doesn't necessary make sense to target some 16 core, 32 thread CPU, when you know that 4 cores is enough.
(As a side note, we limit our engine in released games to 8 threads currently. In internal tools use, the engine is happy to use 128 threads and I actually did some optimizations just a while ago to make it work in a particular case on 64 thread Threadripper, where the unoptimized code was actually faster running 16 threads than even 32.)
-JLarja
> Dummond D. Slow (mental.delete@this.protozoa.us) on November 18, 2020 7:48 am wrote:
>
> > I hope eventually we get some very comparable HT/noHT CPU in AnandTech benchmark for comparing,
> > in the meantime I found this https://www.anandtech.com/bench/product/2622?vs=2652
> > Skylake @ 3,8-4,2GHz 4c/4t versus 4,0-4,2 4c/8t (sadly also has more L2 cache due to Intel's segmenting).
>
> It's something in the pipeline. Generally gaming will benefit turning off SMT even.
It is very simple why gaming often benefits from turning SMT off: it's common to have one or two threads that limit to overall performance, and anything that has even a change to slow those down is bad.
Modern game engines are a bit less affected by this than older ones, but that's mostly because they can better compensate by running other stuff in parallel (e.g. if an old engine could maybe benefit from couple of threads in addition to those one or two limiting threads, maybe a modern engine can use five. Figures are an example, actual values vary).
It's also good to note that games in general aren't optimized to go as fast as they can. They are often optimized to run at most 60 FPS or as low as 30 FPS. So when e.g. multi-threading is considered, it doesn't necessary make sense to target some 16 core, 32 thread CPU, when you know that 4 cores is enough.
(As a side note, we limit our engine in released games to 8 threads currently. In internal tools use, the engine is happy to use 128 threads and I actually did some optimizations just a while ago to make it work in a particular case on 64 thread Threadripper, where the unoptimized code was actually faster running 16 threads than even 32.)
-JLarja
