Does Hyperthreading reduce DCS performance? - ED Forums
 


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Old 08-09-2018, 05:55 PM   #1
jetsimace
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Default Does Hyperthreading reduce DCS performance?

I was wondering if Hyperthreading (2 threads per core) will decrease performance in DCS. Afaik DCS - including 2.5 - will only utilize 2 threads (one main and one for sound). Given that, I assume that having more than let's say 3 or 4 cores (1 or 2 additional cores than DCS requires might be needed for Windows background tasks).
So if one core needs to handle two threads instead of only one it should be slower in execution, right? Also having a higher single core frequency should be better than having more cores.

(Reason why I am asking are the recently annnounced Core i9 9900K with Hyperthreading and Core i7 9700K without)
Does anyone has tested this?
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Old 08-09-2018, 06:01 PM   #2
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I ran with HT disabled for many years until recently. I enabled it again before the summer as DCS have started to utilize more threads. So no, HT does not reduce preformance but increases performance. At least on my rig.
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Old 08-09-2018, 07:31 PM   #3
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DCS uses much more than 2 threads, but 4 cores are still enough. Over all, DCS uses only 25% on my six-core CPU. HT can lower perfomance if an application uses thread instead core(in 2 core processor 0 and 2 are cores and 1 and 3 are threads). So check affinity mask on a processor with HT.
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Old 08-10-2018, 02:39 AM   #4
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Turn the Hyperthreading off, run DCS and check the CPU utilization. If at 100%, turn the Hyper on. You have to fill the physical cores before to fill the others. Hyperthreading improve the performance by 20% when all cores are used.

Don't know if i'm right,i think running an aircraft in DCS needs 2-3 cores.
Then, you have to addition more cores to run the objects depending on your appetite.
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Old 08-10-2018, 12:57 PM   #5
etherbattx
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Default Does Hyperthreading reduce DCS performance?

HT is only useful on some compute tasks. intel added it for servers doing batch work loads. games, and in general, don’t have those types of tasks.

so HT will probably not improve your fps. it depends on the structure of the task and whether the virtual thread can utilize the same cache as the physical thread and make use of a shared bus.

also, if you overclock your cpu, you can achieve higher OC’s by turning HT off.

since most games need more Ghz, instead of more threads, there is an advantage in turning HT off and OC’ing your cpu.

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Old 08-10-2018, 02:16 PM   #6
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I use process lasso to force DCS onto physical cores only. I’ve noticed it doesn’t change FPS whether on or off, but I get significantly more stuttering when I allow DCS to use logical cores (HT on)
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Old 08-10-2018, 03:02 PM   #7
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With DCS I've never had any difference between HT on or off, in term of performance (fps) or stutters. Since 1.5 when I started having an eye on it, till now.

On other sim it can be critical, but with DCS and my settings, I've never had a difference.

Actually with DCS there are case when (with HT on) a logical core can be maxedout, limiting logically the performances, f.e in PG map, but I don't know if disabling HT improve things (I don't have PG map).

BTW talking about what logically happens with cpu usage and hyperthreading in actual DCS is tricky, as usage doesn't seem to behave logically because :
1) different features/technologies with different DCS maps so different behaviors
2) probably the engine is already evolving with vulkan use in aim, and what will be improvements when ready is actually doing weird things with cpu usage.

In comparaison DCS 2.5.0 was behaving logically, perfomances being capped by : 1) fps cap (manually defined, or vsync, or VR), 2) hardware usage when topping 99% with gpu or cpu 1 core/thread or even all cores (it was possible with 2.5.0)

Actually DCS can put gpu to 99% without trouble, but not cpu (even with gpu room and no fps cap, the cpu refuses to go max). But even with strange behavior the performances, to me, are really OK. And I guess the situation is under control by ED.

But it's actually hard to make definitive statements about cpu "settings" and performances. (even cpu clockspeed is not making difference when already enough "high")
Only advice I can point about cpu settings is AVX offset : don't use one because DCS uses AVX instructions (or system detects AVX instructuions when DCS is running) and cpu clockspeed decrease (according to how AVX offset is set, mine default is minus 400Mhz) with each instruction, so constantly...
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Old 08-10-2018, 04:52 PM   #8
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Old 08-10-2018, 05:40 PM   #9
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The newer your Intel CPU is the less it seems to matter, it never bothered me tbh, from 2600k-6700k-7700k and now 8700k, I ran all of them with both setups, didnt change much.


What I think is beneficial, is leave HT on and use ProcessLasso once you run DCS + tons of other stuff like streaming, TiR, VR, music, and all those little gadgets we all have. But also, this never made a bad day sunny, it's polishing an already polished car. Some say PL fixed their stutter, that speaks for itself, it wont harm but maybe also wont gain any advantage, try it out, it's FREE, bitsum.com


I would watch the AVX advixce if you are into heavy overclocking. I dont run any AVX offset, not even at 5.2. It chews through all this without hiccups buut the temps go real high, ~85°C. But DCS will never ever get the CPU as hot as a full dose of prime95-AVX enabled
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Old 08-10-2018, 07:27 PM   #10
etherbattx
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Default Does Hyperthreading reduce DCS performance?

let’s not get confused.

you only have a few physical cores that can do actual work.

pretending there is twice as many (HT) almost never results in better performance.

if it did, we could all just pretend there is 100 of them and run mega settings with mega detail at 140fps
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