Hyperthreading V4.1

[OzWhitey 3,353]

Heat is about your overclock, your voltage, the TIM or solder that gets heat away from the chip and your cooling solution. Heat issues aren't caused by the stability of an overclock per se. Often you'll add voltage to try and achieve stability, and that generates heat.

if you turn off hyperthreading, you can get a better clock. I was looking at sone benches for my chip - an ancient 5820k - earlier today. I overclock on water 24/7 at 4.4 Ghz. People who run this single core can achieve  4.9 Ghz,

if p3d only used a single core, it'd make sense to turn of hypethreading. As it uses multiple cores, there's a lot more downside in turning these off, compared to the ten percent of extra clock speed you'd gain.

[JoeFackel 760]

Of course it runs cooler if you reduce it's processing power for about 20%

[SteveW 1,792]

P3D (and other apps) being Multi-threaded is not synonymous with CPUs being HyperThreaded (HT=On).

 

To understand HT simplified, we need to imagine a single core running, let's say, 20 threads. The CPU provides each thread in turn with a little processing time, or time-slice, so they all appear to be running at the same time.

What the CPU has to do is remember information about each thread so that each thread can be restarted where it left off when its time-slice comes around.

Now let's look at  that same core with HT=On. The core appears to the system as two cores (Logical Processors) and the system jobscheduler places threads evenly across those two cores (LPs).

Whatever the distribution, the processing of all threads is only going to happen on that one real core.

So what's the difference with HT enabled? Each LP keeps track of its own threads such that two are handled simultaneously. In effect – the time taken up keeping track of all the threads on the real core is halved. This can amount to as much as 30% increase in processing across the CPU with the right kind of threads.

And that's the catch - "the right kind of threads".

There are threads that can be paired onto the two LPs of an HT enabled core and they work well together collecting data perhaps for another thread. Those same two threads on an HT enabled core outperform the same two threads on the singe threaded HT disabled core every day of the week.

Then there are threads that don’t want to be shared with other processes on a core HT enabled or disabled, they want the core to themselves.

The crunch with HT enabled: Since we have in P3D some threads that want the throughput of the entire core we must preserve that requirement with the Affinity Mask (AM).

Generally the affinity mask will show a binary pair “01” for each core so that each P3D process will occupy only one LP of each core. Where we have a pair of ones “11” both LPs of that core will be loaded with a P3D process. The zeros show LPs masked off or hidden from the process.

P3D will spread out over as many LPs as it finds and so simply enabling HT will likely result in a decrease in the sim performance even though we see an overall increase in the PC performance.

With HT enabled there may be any other kind of process running on the PC that inadvertently doubles the processing requirement - for instance a virus checker may spawn eight processes instead of four with a four core CPU HT enabled.

An example set-up for an 8 core system would be:

Placing P3D on 6 cores 01,01,01,01,01,01,00,00 = AM 21840 and placing addon exe apps that run along with the sim on the other two cores 00,00,00,00,00,00,11,11 works well.

 

The increases seen in core temperature when using HT enabled is because, first of all there is more hardware to get hot, the hardware that reduces the thread switching time – more work done = more heat. Secondly, uncontrolled doubling of processes on that core contributes to massive heat increase. With P3D in the scenario loading phase this could be excessive with incorrect AM.

With the overclock the position on the heat curve is important that we set it so that HT can be accommodated or we must turn off HT and multi-threading performance is lost due to thread switching time doubling.

HT off can mean the CPU is able to clock higher but in the big P3D system, networking and multi-threading is important. The trade-off against losing HT performance for an extra few MHz CPU clock should be carefully compared.

 

 

[OzWhitey 3,353]

6 minutes ago, SteveW said:

we must preserve that requirement with the Affinity Mask (AM).

I don't run an affinity mask in P3D, and I'm not convinced it would help, though I also don't know that it doesn't.

Has anyone actually tested this properly  in v4/4.1, and was there any quantifiable difference?

[SirStiggie 63]

2 hours ago, aushie said:

Asus Z97 A

Easy way to do it is to use AI Suite III and have it do the overclock for you. Once you find a setting that gives you the balance between stability and performance, put them in manually in the bios. I'm lazy which is why I did it that way :)

 

[SteveW 1,792]

9 minutes ago, OzWhitey said:

I don't run an affinity mask in P3D, and I'm not convinced it would help, though I also don't know that it doesn't.

You saw the posts from LM stating they have threaded-out more stuff? So with no AM two threaded-out parts might occupy the same core (HT=On). Are you convinced now?

[OzWhitey 3,353]

9 minutes ago, SteveW said:

You saw the posts from LM stating they have threaded-out more stuff? So with no AM two threaded-out parts might occupy the same core (HT=On). Are you convinced now?

Umm...no. No, not at all. Affinity masks have been a contentious topic for many years, and I know you're a fan of them.

As per my last post - have either you, or anyone else, actually tested performance before and after affinity mask application in v4/4.1? Until someone has done this , and has some quantifiable data to report, it's very hard to know if it will help or hinder the program's real-world performance. 

[SteveW 1,792]

 

5 minutes ago, OzWhitey said:

Umm...no. No, not at all. Affinity masks have been a contentious topic for many years, and I know you're a fan of them.

Affinity Masks are to avoid heat in the basic sense and are a requirement. Even if you do not assign an AM your four core will be AM=15, with  HT enabled your AM=255. With your 6 core your no AM = 63, and so on. There's no such thing a no AM. All an AM does is present a number of LPs to a process like a four core CPU presents four. 

I'm simply talking about gravity - the apple tends to fall to the ground. In Flight sims, PCs are not always the same and some people find their apples fall upwards.

The logical conclusion is that with HT=Off there need not be an AM to see threaded-out parts moved onto another actual core.

.

 

[AnkH 2,232]

48 minutes ago, David Roch said:

So talking about "stable OC" when changing a main component temperature makes no sense.

So, then to you it makes more sense to talk about "stable OC" if you turn off basically what makes an i7 and i7 (HT, otherwise you could use an i5...) and overclock like this? Sorry, but no. A "stable OC" to me is using the processor as it is designed, means HT on for an i7.

Besides that, what do you gain? Probably some 200-300MHz on four cores. I tell you something: whether your i7 runs with HT on and 4.5GHz or HT off and 4.8GHz will provide you with a phenomenal 7% more FPS in the absolut best case. Means: in a situation where you get 20FPS with HT on and 4.5GHz, you will get 21FPS with HT off and 4.8GHz. What a tremendous benefit. Even if you might be able to increase your clocks to 5GHz due to HT off, you will end up with only 2FPS more. Is this really worth turning HT off? I guess no...

[srce 54]

2 hours ago, charliewards said:

What setting do you use in AF to achieve this? 

The second bit (from the right) should be 0.

I have 20 logical cores, so use: 1111 1111 1111 1111 1101 - 1,048,573

40 minutes ago, OzWhitey said:

I don't run an affinity mask in P3D, and I'm not convinced it would help, though I also don't know that it doesn't.

as anyone actually tested this properly  in v4/4.1, and was there any quantifiable difference?Has anyone actually tested this properly  in v4/4.1, and was there any quantifiable difference?

For me, there is a measurable difference disabling logical core 1.  It also appears to be beneficial to keep the other logical cores enabled. YMMV.

[OzWhitey 3,353]

Now I'm confused. I thought you were arguing that we needed to apply a non-default affinity mask to our sim, which is why I was asking for data.

if you're just arguing that affinity masks are there anyway, and there's a default setting that uses all the cores and is applied when we don't do anything then, ok, sure.

Also:

"With your 6 core your no AM = 63, and so on. There's no such thing a no AM."

Wait, what??? I think you just divided by zero there. 😳😳😳

😊

[brucets 94]

Okay, bottom line -- I have an unclocked I7-7700k. What do I do??

I fly FSX right now, but will probably go to P3D in the not to distant future.

HT ON or Off and what AM??

Thanks,

Bruce

[OzWhitey 3,353]

11 minutes ago, AnkH said:

A "stable OC" to me is using the processor as it is designed, means HT on for an i7.

That's not how anyone who does overclocking defines a stable overclock. Stable overclock means putting the CPU under stress, without adverse effects occurring. Running the overclock using Prime95 or a similar program for a certain period of time would be a common definition.

The term can also be used to mean an overclock that doesn't crash in longer-term real world use.

[SteveW 1,792]

Just now, srce said:

For me, there is a measurable difference disabling logical core 1.

Good post. With P3D the threaded out parts reduce the overhead in the main thread located on the first LP presented. And so disallowing one HT LP of the first core ensures the threaded-out parts do not occupy the core with the main thread allowing for the performance improvements.

 

3 minutes ago, OzWhitey said:

"With your 6 core your no AM = 63, and so on. There's no such thing a no AM."

Wait, what??? I think you just divided by zero there. 😳😳😳

😊

Binary 111111=Dec63=Hex3F. You've clearly not been doing your homework.

[simbol 5,767]

2 minutes ago, brucets said:

Okay, bottom line -- I have an unclocked I7-7700k. What do I do??

I fly FSX right now, but will probably go to P3D in the not to distant future.

HT ON or Off and what AM??

Thanks,

Bruce

OC if posible to minimun 4.6GHZ, user proper cooling (Water is the best but not necesary) and leave HT ON.

The last step is to "Enjoy your flights"

Best Regards,

Simbol