Sign in to follow this  
Rockliffe

Advice on hyperthreading

Recommended Posts

Hey guys, can anyone offer some advice on whether I should have hyperthreading switched on or off with my new i7-6700k build. I run FSX-SE and have always understood that hyperthreading is redundant with FSX as it only runs on a single core. However, is that still the same train of thought or is there a good reason for running hyperthreading. I have previously run with a i5-2500k when I had AffinityMask =14. What should I do in this area, bearing in mind I'm running FSX-SE with a i7-6700. Thanks.

Share this post


Link to post
Share on other sites
Help AVSIM continue to serve you!
Please donate today!

 I run FSX-SE and have always understood that hyperthreading is redundant with FSX as it only runs on a single core.

 

 

 

Not true, FSX runs on all cores. That's since Aces gave us the service packs years ago. The bulk of the work is on one core though. 

 

6700K all cores utilised but the other four virtual cores of little benefit. So depends what you do with your rig. For me, rarely sim these days so keep HT on. I don't think there are any application I run that benefit from HT, but my rig runs great anyway, overclocked with low temps, so I leave it on. 

 

There are some that claim scenery loads faster with HT on, but not definitive. If overclocking, HT off will drop the CPU temp by 10 degrees or so and enable a higher overclock. The higher overclock is probabaly more advantageous than an unconfirmed minor benefit from HT on.

 

That's my take on it anyway.

Share this post


Link to post
Share on other sites

Not true, FSX runs on all cores. That's since Aces gave us the service packs years ago. The bulk of the work is on one core though. 

 

6700K all cores utilised but the other four virtual cores of little benefit. So depends what you do with your rig. For me, rarely sim these days so keep HT on. I don't think there are any application I run that benefit from HT, but my rig runs great anyway, overclocked with low temps, so I leave it on. 

 

There are some that claim scenery loads faster with HT on, but not definitive. If overclocking, HT off will drop the CPU temp by 10 degrees or so and enable a higher overclock. The higher overclock is probabaly more advantageous than an unconfirmed minor benefit from HT on.

 

That's my take on it anyway.

 

Interesting. That's helpful information Martin, appreciated. So if I set hyperthreading on, what value should I set with AffinityMask?

Share this post


Link to post
Share on other sites

Howard,

 

Whether or not you run with Hyperthreading on or off depends on what other programs are running while you're flying.  If pretty much nothing else, then I'd say off.  In fact, off is usually the preferred, best performing setting.

 

The AF settings... there is an excellent description of AF in the AVSIM Setup Guide (located on the Top Right of all AVSIM pages which explains AF, so users can determine the correct value and set it themselves.  I think this is important to understand AF and what it does if one is going to stay in our hobby.

 

My very best wishes to you!

Share this post


Link to post
Share on other sites

For 6700K,  AM=85 works well (I'm currently using) and others like AM=116 (I used to use).

 

Jeff

Share this post


Link to post
Share on other sites

Howard,

 

Whether or not you run with Hyperthreading on or off depends on what other programs are running while you're flying.  If pretty much nothing else, then I'd say off.  In fact, off is usually the preferred, best performing setting.

 

The AF settings... there is an excellent description of AF in the AVSIM Setup Guide (located on the Top Right of all AVSIM pages which explains AF, so users can determine the correct value and set it themselves.  I think this is important to understand AF and what it does if one is going to stay in our hobby.

 

My very best wishes to you!

Thanks for the information Dave

 

For 6700K,  AM=85 works well (I'm currently using) and others like AM=116 (I used to use).

 

Jeff

Cheers Jeff.

. Appreciated. I'll check out the guide in detail.

Share this post


Link to post
Share on other sites

Networking and disk I/O are deeply multi-threaded and the Windows system as a whole benefits from HT enabled. If this was not the case we would know about it by now. Turning off HT on my 3960x delivers a noticeably stodgy performance compared to an obviously more zesty HT on. The problems come from the way certain apps utilise CPUs and most problems come from processes that don't consider two Logical Processors sharing the same core. FSX and FSX:SE consider the Hyperthreading mode but Prepar3D does not, so with P3D we need an AM for HT enabled or it will make double the processes per core in HT mode. On the four core with HT enabled you will see that FSX:SE uses AM=85. The real task is making sure apps running on the PC alongside FSX occupy the last two cores (last 4 LPs) and keep off the first two cores (first 4 LPs). If you're running addons that use SimConnect that means Networking, and so that aspect alone is improved with HT enabled. It is true that FSX and P3D utilise a monolithic thread design whereby they do not care about HT, but running on a properly set up HT system they run better by at least 5% or more. On a professional test harness these sims perform better with 5% more background throughput and HT enabled than they do with 5% overclock and HT disabled.

Share this post


Link to post
Share on other sites

Networking and disk I/O are deeply multi-threaded and the Windows system as a whole benefits from HT enabled. If this was not the case we would know about it by now. Turning off HT on my 3960x delivers a noticeably stodgy performance compared to an obviously more zesty HT on. The problems come from the way certain apps utilise CPUs and most problems come from processes that don't consider two Logical Processors sharing the same core. FSX and FSX:SE consider the Hyperthreading mode but Prepar3D does not, so with P3D we need an AM for HT enabled or it will make double the processes per core in HT mode. On the four core with HT enabled you will see that FSX:SE uses AM=85. The real task is making sure apps running on the PC alongside FSX occupy the last two cores (last 4 LPs) and keep off the first two cores (first 4 LPs). If you're running addons that use SimConnect that means Networking, and so that aspect alone is improved with HT enabled. It is true that FSX and P3D utilise a monolithic thread design whereby they do not care about HT, but running on a properly set up HT system they run better by at least 5% or more. On a professional test harness these sims perform better with 5% more background throughput and HT enabled than they do with 5% overclock and HT disabled.

That's really helpful information Steve, thanks. So should FSX-SE work on core 1, or does the PC decide where it will run while using other cores when needed? Sorry, I'm a little ignorant in this area of FSX!

Share this post


Link to post
Share on other sites

FSX makes good use of multi core and HyperTreading but when you get past 3 cores it is only improving ground texture loading. I've just been playing around a bit with my 6700K recently and without HT activated (with appropriate AM) I find it horrible for photo scenery. You can't fly very fast with a high LOD without getting blurries. With HT on (and appropriate AM) it is a lot better but still not as good for ground texture loading as my 6 core SandyBridge-E with HT on. That is despite the Skylake having a higher overclock than the SandyBridge-E.

 

But when it comes to FPS the Skylake is very noticible better with its beter architecture, DDR4 and higher overclock. (Give me Skylake-E soon please Intel...)

 

AM=85 is the FSX default for a quad core HTon. That's what you get if you don't put anything in the .cfg.

 

For a quad core I find AM=241 is the best all-round AM with HTon  whilst AM=249 works even better with some photoscenery but has the potential to not work so well depending on if you get any other CPU intensive activity running. (UK photoscenery with treescapes for example generates high CPU load on the FSX thread that loads pretty much everything that is read from your harddrives). I would also imagine any Wx software that generates a lot of cpu load at times injecting Wx might not work that great with AM=249.

 

If you activate HT and use AM=84 it is the equivalent of HToff AM=14.

Share this post


Link to post
Share on other sites

FSX makes good use of multi core and HyperTreading but when you get past 3 cores it is only improving ground texture loading. I've just been playing around a bit with my 6700K recently and without HT activated (with appropriate AM) I find it horrible for photo scenery. You can't fly very fast with a high LOD without getting blurries. With HT on (and appropriate AM) it is a lot better but still not as good for ground texture loading as my 6 core SandyBridge-E with HT on. That is despite the Skylake having a higher overclock than the SandyBridge-E.

 

But when it comes to FPS the Skylake is very noticible better with its beter architecture, DDR4 and higher overclock. (Give me Skylake-E soon please Intel...)

 

AM=85 is the FSX default for a quad core HTon. That's what you get if you don't put anything in the .cfg.

 

For a quad core I find AM=241 is the best all-round AM with HTon  whilst AM=249 works even better with some photoscenery but has the potential to not work so well depending on if you get any other CPU intensive activity running. (UK photoscenery with treescapes for example generates high CPU load on the FSX thread that loads pretty much everything that is read from your harddrives). I would also imagine any Wx software that generates a lot of cpu load at times injecting Wx might not work that great with AM=249.

 

If you activate HT and use AM=84 it is the equivalent of HToff AM=14.

Thanks matey, helpful advice. Appreciated.

Share this post


Link to post
Share on other sites

That's really helpful information Steve, thanks. So should FSX-SE work on core 1, or does the PC decide where it will run while using other cores when needed? Sorry, I'm a little ignorant in this area of FSX!

Remember that FSX:SE does not take notice of the AffinityMask setting in the .cfg, only FSX and P3D read this in and adjust accordingly. FSX:SE will do it's own thing unless manipulated by another program.

Share this post


Link to post
Share on other sites

Remember that FSX:SE does not take notice of the AffinityMask setting in the .cfg, only FSX and P3D read this in and adjust accordingly. FSX:SE will do it's own thing unless manipulated by another program.

Ah, so are you saying it's pointless to ad any such line to the cfg? I know that's what I thought you said....

Share this post


Link to post
Share on other sites

 

...The sim looks at the CPU and lays out it's main worker processes. It hopes that you have four logical processors, if not it places these together on less logical processors (LPs). That's why we specify AM=85 or AM=116 because these provide four unmasked logical processors. In binary 85=01010101 but since we are talking about a CPU with HyperThreading we place a comma between each pair (desktop CPUs we use have two per core) like this: 01,01,01,01 (some CPUs have more than two LPs per core - four per core on a two core AM=113=0111,0001). The first one the right (the first LP unmasked by a one is on core zero in this case) is where the first worker process is started and does the main work of rendering. We can get motherboards that can overclock just one core if we want and we would overclock this one. The other three (or more) worker processes (on those cores with an LP unmasked) do the background work. The second worker process manages the other processes and communicates with the first on a timely basis - so we keep other processes off of the cores of the first two unmasked LPs.

Share this post


Link to post
Share on other sites

Suggest you run Task Manager \ Performance tab along side FSX to see which processors are getting used.

 

That gives you a real time view.

 

If you change AM, you should see the corresponding change in the Task Manager graphs.

Share this post


Link to post
Share on other sites

Remember that FSX:SE does not take notice of the AffinityMask setting in the .cfg, only FSX and P3D read this in and adjust accordingly. FSX:SE will do it's own thing unless manipulated by another program.

 

This is news to me. Where did you get this information?

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this