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davidzill

Hyperthreading (Topic revived)

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How many of you have hyperthreading on in your BIOS, and what are your performance results in FSX? I ask because I've always had it off because I was under the impression FSX did not support its use...until recently. I installed PREPAR3D V4 yesterday, and was perplexed at how I was only getting frames with default settings at between 15-24 FPS on a I7 4790K @ 4.9 Ghz w/ 16 GB DDR3 RAM, and (2) 1080 GTX's.

 I posted and through a lengthy discussion someone asked if hyperthreading was on or off. I turned it on and immediately, I saw my frames jump to about 100+.

I was concerned with how FSX would be effected by hyperthreading, so I went in and started with the PMDG NGX at Flightbeam's KSFO, taking off and flying a wide circuit and ILS approach to 28L in weather and fog (REX TD 2048x 2048 clouds. Results? I was able to keep my FPS capped at 60 FPS. In and near the airport, the FPS would obviously dip well below 60 (30-35 FPS), but one would expect annoying and prominent skipping and stuttering. I was surprised to notice Track IR panning was as smooth as silk, and even with the dip in FPS from 60, I didn't notice any apparent stuttering, and I was looking very hard for it. It was as if something was working to sync the display performance. On approach, I would look down at building, everything looked smooth. Keeping my fingers crossed. 

Prior to turning on hyperthreading, I had the Affinitymask=14 in the FSX.cfg. Frames were locked at 30 and considerably smooth in fight, with frames dropping to a stuttery 15-24 FPS at Hifi scenery. I understood this as for many being the best balance of graphics and performance. I could taxi and watch the taxiway lights, literally counting the frames as the taxiway lights stuttered their way by. After turning on hyperthreading, I changed Affinitymask=14 to 84. CPU temps were nominal, never going above 55c (I have a water cooler). 

From my understanding, FSX has never supported hyperthreading, UNTIL...the Core I7 processors were released. 

 

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I don't think hyperthreading is something an application "supports" or not - it's just whether the architecture of the application can take advantage of it. The virtual HT cores show up in Windows as if they're physical cores - the hardware controls the flow of data between the two types of cores, I don't think the application or OS even know the difference. The virtual cores are essentially just the idle cycles of the physical cores that exist in between instructions, which the CPU can use to run parallel threads - if the application can't take advantage of parallel processing, then HT is going to be of little use for it.

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