# CPU hyper threading



## fraz (Apr 21, 2018)

Hi,

Hope this is in the right forum - Please confirm !

Sometimes, when people don't get the expected performance from a CPU, other mention disabling hyper threading.

If we take a 4 core 8 thread CPU with hyper threading disabled, does this mean suddenly the CPU is only acting as a 4 core 4 thread CPU?

If this is the case can the CPU still perform to its capability (max output) if used like this?

Thanks


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## Divico (Apr 21, 2018)

fraz said:


> If we take a 4 core 8 thread CPU with hyper threading disabled, does this mean suddenly the CPU is only acting as a 4 core 4 thread CPU?


Yes exactly.


fraz said:


> If this is the case can the CPU still perform to its capability (max output) if used like this?


Well depends. Hyperthreading means youre splitting up the cpu power into more threads than phsysical cores which improves multitasking. This of cause means that the program you are working with is asigning tasks to the threads evenly. When it comes to realtime performance when for example using lots of VSTis or mixing plugins this is really useful.

As far as I understand this deactivating hyperthreading can be usefull when you do not need so much multitasking and want your cores to perform at max efficiency.


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## tack (Apr 21, 2018)

Once upon a time, hyperthreading was horrible. It was implemented poorly in hardware, and very poorly supported in operating systems.

Since Nehalem, now released almost 10 years ago, hyperthreading hardware implementations have been actually good. And OS schedulers now know how to deal with hyperthreads. In the past 5 years, the arguments in favor of disabling it have gotten extremely weak.

There may be some pathological cases where disabling hyperthreading can result in better performance. But 99% of the time the cost-benefit is really clear. Disable hyperthreading is something to try when you're diagnosing a performance problem. But if you do it preemptively without anything to measure against whether or not it's helping, you are neutering a significant chunk of your processor's performance.


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## chimuelo (Apr 21, 2018)

I doubt anyone here layers 4 Horn Sections, 3 E. Pianos, acoustic pianos, multiple Diva filters on Z2HZ, string libraries, etc.
High polyphony from sustain work can beat up a CPU if not careful.
With HT disabled I get the best performance.
Every time I build a new rig and delegate the old ones to spares I check out the CPUs newest “helpful” features.
I end up shredding them in the motherboards BIOS.
Just like my Operating System, the more I disable the better off for me.

DAW builders I converse with say it’s because I’m using Core locked synths like Z2HZ.
Extending the Cores instruction capabilities with HT means the most active vote gets scheduled first, which just doesn’t help me.
By disabling HT new instructions go to other cores instead of trying to use “boost” or HT.
Turbo boost operates the same way, taking the busiest core and extending its frequency.

If I were using just Kontakt things might be different. Maybe HT on my next build, especially if Zebra3 is not Core locked. But until then don’t need the extra help.


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## tack (Apr 21, 2018)

If you have idle real cores, threads will get scheduled to them before going to hyperthreads. Back before schedulers were sufficiently HT-aware, yes, those kinds of shenanigans definitely happened.

I did a quick test with Z2HZ. CSBO innocent patch, voices set to many, accuracy set to divine. On my 8700K with Windows 10 and Reaper, I managed the same polyphony count with HT disabled as I did with it enabled. (15. At 16 it crackled in either case.)

If you've truly absolutely no need for the additional multiprocessing headroom then, ok, sure, I'll grant you the the argument that you may as well disable it to scratch around the margins of that performance benefit. I'd guess you're throwing away something like 30-40% multiprocessing performance for 2-3% single core performance. I doubt that tradeoff is smart for most of us. But I know chimuelo does a lot of live work where that exchange could make perfect sense.


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## chimuelo (Apr 21, 2018)

I’m jealous.
The i7 8700k, Windows 10 and Supermicro X11SC-F w/ Q370 is my next 1U.
I’m on H97 Server board and i7 4790k.
Been using 4790k for years now.
The latest build is less than a year old, but I really beat up CPUs for hours every day and night.
It’s my last new 4790, so I’m skipping over discontinued 6700s, 7700s and heading for the 8700.
Really wanted a Xeon E HEDT. But appears that “leak” was incorrect.

That’s good to hear and thanks for testing the Zeb.
Still the only soft-synth I own that can hang in with hardware on large Arrays.
Even the Mighty Omni no longer gets used for analog-ish tones. Strictly Keyscape and Granular.

Looking forward to upgrading and becoming current.
I’m so busy I can’t get time to jump all of my rigs to Windows 10.
I’m always a few years behind.

Cheerz


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## DAW PLUS (May 2, 2018)

Typically, HT should offer more performance. Locked synths may be a rare occasion where it hurts performance, but I haven't seen this in 8 years of testing. I suspect most of HT issues are configuration dependent.


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## Divico (May 2, 2018)

DAW PLUS said:


> Typically, HT should offer more performance. Locked synths may be a rare occasion where it hurts performance, but I haven't seen this in 8 years of testing. I suspect most of HT issues are configuration dependent.


I guess as soon as one uses a bunch of synths at the same time its irrelevant anyways


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## Piano Pete (May 2, 2018)

In my own tests, I have not seen any benefit worthwhile to disable this. Maybe once upon a time, but definitely not in the past 3-6 years. 

If you are trying to squeeze out percentage points of potential performance, you are throwing away other very useful things in the process. I have yet to see increased performance doing this on PCs, and if you are honestly running into problems where that is your solution, I would recommend a plethora of other fixes and potentially just purchasing a better cpu.


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## DAW PLUS (May 3, 2018)

Divico said:


> I guess as soon as one uses a bunch of synths at the same time its irrelevant anyways


Actually, on average, HT boosts performance on audio systems by 25%. It does pay off... 
We are just testing new configurations, I'll keep an extra eye on HT and Zebra.


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## Divico (May 3, 2018)

DAW PLUS said:


> Actually, on average, HT boosts performance on audio systems by 25%. It does pay off...
> We are just testing new configurations, I'll keep an extra eye on HT and Zebra.


I think you misunderstood me  My point was that even if disabling HT can give you a small performance boost for certain applications, using several tracks and plugins at once will DEFINETLY benefit from HT and disabling it will cut your performance! Unless your DAW doesnt handle multicore usage properly. But as far as I know thats not a problem nowadays. Reaper for example tries to give each track its own core and keep all of them working more or less the same amount.


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## DAW PLUS (May 3, 2018)

Divico said:


> I think you misunderstood me  My point was that even if disabling HT can give you a small performance boost for certain applications, using several tracks and plugins at once will DEFINETLY benefit from HT and disabling it will cut your performance! Unless your DAW doesnt handle multicore usage properly. But as far as I know thats not a problem nowadays. Reaper for example tries to give each track its own core and keep all of them working more or less the same amount.


Actually I just filled you in, we are on the same line. 
All DAWs use multithreading, the worst I have seen is support for 15 cores but it works excellent with VEP to fill in the other cores (tested on dual 12 core system). Cubase with ASIOguard handles 32 virtual cores like most other DAWs. New development seems to shift a bit on various DAWs, I am currently looking at the various DAW versions.


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