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  • Please see the most recent updates in the "Where did the .com name go?" thread. Posts number 16 and 17.

    Post 16 Update

    Post 17 Warning

Hyper-Threading

falcon409

falcon409

SOH-CM-2025
Should I be running hyper-threading for Flightsim with a quad-core system or is it just a lot of hype and little substance?
 
The consensus is that hyperthreading is all hype when it comes to MicroSoft's flight sims. Most people seem to get smoother performance with hyperthreading turned off.
 
According to a series of articles by Doug Horton in Computer Pilot Magazine the single most important item as far as performance in FSX is the speed of your processor. In multicore processors that means Core 0 or the first core. The second core might chip in a little, but FSX was not designed with multicore processors in mind so hyperthreading isn't going to do much good. Maybe Lockheed/Martin will push Prepar3d over that hump if they haven't already.
 
falcon409 said:
Should I be running hyper-threading for Flightsim with a quad-core system or is it just a lot of hype and little substance?
Click to expand...

Just for FS2004 or FSX there is no use of HT. Turning HT on just uses more energy (at least in theory) and produces thus more warmth. If some other programs (you are using) don't benefit it remarkably, turn it off (it can be done in BIOS setup).

Pekka
 
You know, I wonder if it's all a bit of hooey. I rebuilt my FSX.cfg last week as I was getting OOM errors after pfaffing about with OCing. Anyway that is an aside, I went back to unclocked. I reset my bios to default which of course included hyperthreading my quad core I7 2600K CPU. I sent the cfg off to Jesus's website for it's twiddly twiddly thing and put the new one back into FSX.
The following day I went back and switched off the HT in bios. I went back to flying FSX and it was only when I saw this thread did I realise I had not altered the cfg to reflect the lack of HT.....
So this meant I was using a setting of AffinityMask=84 when it should have read AffinityMask=14. But you know there was no discernible difference in the quality or rate at which the sim ran. I have followed convention and just in case set AffinityMask=14.
I rest my case M'Lud. Hooey. :jump:
 
johannesl said:
According to a series of articles by Doug Horton in Computer Pilot Magazine the single most important item as far as performance in FSX is the speed of your processor. In multicore processors that means Core 0 or the first core. The second core might chip in a little, but FSX was not designed with multicore processors in mind so hyperthreading isn't going to do much good. Maybe Lockheed/Martin will push Prepar3d over that hump if they haven't already.
Click to expand...

That was true of FSX in its original form, but MicroSoft added multi-core support to FSX with FSX Service Pack 1. That is why so many people saw tremendous frame rate improvement and smoother performance when they installed SP1. Hyperthreading does not help FSX because hyperthreading simply takes each physical CPU core and divides it into two virtual cores. FSX only recognizes physical cores.
 
Hyperthreading? Not on my rig!
IF an application IS heavily threaded, which our sims are not, HT can be of great benefit.
On a Quad Core CPU that is HT capable, there are still only 4 Physical Cores.
Each Physical Core includes a single Physical Execution Unit(PEU).
The two Virtual cores(VC1, VC2), the second of which is enabled with HT=ON, share the PEU.
View attachment 86988
With HT=On, the PEU data threads flip-flop between VC1 and VC2. While one Virtual Core is processing data, a miniscule wait state is generated, and data is held in a buffer, until the PEU addresses the other VC
With HT=ON, if both Virtual Cores, of a Physical Core, are given affinity to FSX, basically there should be very little harm done, because FSX has exclusive use of the PEU and FSX "only" data is being processed.

Most of us limit use of other applications, and minimize background apps, while running our sims, so, in reality, a proper Affinity Mask can alleviate most HT=On bottlenecks.

Also with HT=ON, because of the flip-flop of VC1 vs VC2, there may be an overclocking limitation if the silicon isn't fast enough during switching. No Switching=No Delay. No Delay=Faster...Don
 
fxsttcb said:
Hyperthreading? Not on my rig!
IF an application IS heavily threaded, which our sims are not, HT can be of great benefit.
On a Quad Core CPU that is HT capable, there are still only 4 Physical Cores.
Each Physical Core includes a single Physical Execution Unit(PEU).
The two Virtual cores(VC1, VC2), the second of which is enabled with HT=ON, share the PEU.
View attachment 86988
With HT=On, the PEU data threads flip-flop between VC1 and VC2. While one Virtual Core is processing data, a miniscule wait state is generated, and data is held in a buffer, until the PEU addresses the other VC
With HT=ON, if both Virtual Cores, of a Physical Core, are given affinity to FSX, basically there should be very little harm done, because FSX has exclusive use of the PEU and FSX "only" data is being processed.

Most of us limit use of other applications, and minimize background apps, while running our sims, so, in reality, a proper Affinity Mask can alleviate most HT=On bottlenecks.

Also with HT=ON, because of the flip-flop of VC1 vs VC2, there may be an overclocking limitation if the silicon isn't fast enough during switching. No Switching=No Delay. No Delay=Faster...Don
Click to expand...

And does that apply to those of us who use DCS as well??
 
DaveKDEN said:
Since I've never investigated it, how do I tell whether HT is on or off?
Click to expand...

Open Task Manager -> Performance Tab

HT is off on my machine and I see 4 (quad) cores in the CPU Usage History. If HT is on, then you'll see 8 . . . I think that's correct. At least more than 2 or 4 for sure, depending on your CPU.
 
Dumonceau said:
And does that apply to those of us who use DCS as well??
Click to expand...
Dunno about DCS, but, it basically applies to any application that is not highly threaded. Mebbe a DCS user that has tried it on/off can enlighten us. Very few games, that I'm aware of, can actually use the benefits of HT...Don
 
gecko65 said:
Open Task Manager -> Performance Tab

HT is off on my machine and I see 4 (quad) cores in the CPU Usage History. If HT is on, then you'll see 8 . . . I think that's correct. At least more than 2 or 4 for sure, depending on your CPU.
Click to expand...

Thanks. I have a trusty old Quad core Q6600 o/c's to 3GHz. I see 4 graph quadrants running in the performance tab CPU history, so I guess HT is off.
 
DaveKDEN said:
Thanks. I have a trusty old Quad core Q6600 o/c's to 3GHz. I see 4 graph quadrants running in the performance tab CPU history, so I guess HT is off.
Click to expand...

Sounds like it. If I remember correctly, you can turn HT on/off via the BIOS setup.
 
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