CAVEAT : I am not responsible for any data loss, device malfunction, divorce, flood, job loss, penile retraction or any other event that might happen as a result of embarking on this quest. I advise you conduct proper research on the subject before taking any steps on your computer

Hyper-threading is Intel's proprietary simultaneous multithreading (SMT) implementation used to improve parallelization of computations (doing multiple tasks at once) performed on x86 microprocessors. (Definition from Wikipedia)

For each physical core on your CPU's processor, the operating system addresses two virtual cores and shares the workload between them when possible.

In layman terms, assuming your CPU is a bus with 4 seats, Intel's conductor puts two passengers on each seat so the bus can transport 8 passengers at once. The bus performs like an 8 passenger vehicle when it is actually a 4 passenger vehicle.

A processor might be able to perform 4 arithmetic operations every clock cycle, yet be limited to 2 operations per cycle by nature of the running program. This would leave 2 idle “slots”, which wastes performance. Hyperthreading attempts to fill these slots by running another program at the same time. (I culled this part from an answer on Quora)

Hyper-threading works on the basis that there would be stall times where the cores are idle and tries to maximise efficiency by adding extra threads when possible. Continuing with the analogy, the conductor checks each passenger boarding and tells the slim ones to lap each other. The ones with big bodies are allowed to seat alone.

Many apps can benefit from hyper-threading as it increases relative performance, ceteris paribus.

Why you should Turn It Off.

Battery Drain:
There is no free lunch in Freetown. Running your cores at double their capacity implies consuming more power. If you are on a battery powered laptop, this could reach as much as 30% power savings if hyper-threading is disabled.

Temperature :
When a CPU draws more power, it is converted into heat. This makes your computer get hotter and unbearable to lap. Heat savings from disabling hyper-threading can be up to 10C or more.

Gaming
Many games actually benefit from disabling hyper threading. Many gamers have reported increased performance after their hyperthreading has been disabled. This is because hyper threading was designed to maximise efficiency on small and short computes but games do not follow this pattern.

ZombieLoad Attack:
There is an exploit on all intel cpus called the zombieload attack. This attack exploits the core of hyper-threading which combines different processes onto same core and allows data access by an attacker. No matter how strong your encryption keys or operating system is, it could be exploited at the CPU level. All major OS has been tested and they all fail in this regards. It is even possible to read Tor encryptions by an attacker using ZombieLoad. The solution offered has been to disable hyper-threading. It is recommended to update your OS with the latest security updates prior.

Disabling Hyper-Threading
Each OS / Device Manufacturer has its own process for disabling hyper-threading and I would advise you consult on this before proceeding.
Follow the official recommended process available on the manufacturer's website. To begin, you can google "How to disable hyper-threading on Bleep" where Bleep is your device name, model and OS.

Discussions on Performance Loss
Intel has stated that a 7% loss in performance should be expected from disabling hyperthreading. Apple was been conservative and said a loss of up to 40% should be expected. This has been discounted by various testers and many people. The intel figures are more realistic from tests conducted in recent studies.

My Own Experience
I disabled hyper threading on a 2012 MacBook Pro, Catalina 10.15.7, (latest security update added) after following Apple's official recommendation and have the result below:
Average: CPU Temp. dropped 10C. I can now easily put my laptop on my bare laps as I work on the bed.
Battery: I have gained more than an extra hour of battery use.
Responsiveness: The laptop does is still very responsive. I have no stuttering issues
Noticeable drawback: To start the laptop, I have to long-press the power button for a few seconds instead of the previous touch and go. Since I hardly shut down my MacBook Pro, this is not an issue. (I usually go many weeks without shutting down the laptop.)

Note:
I run Visual Studio Code with Sveltekit, Firefox Developer Edition with 4 tabs, Safari with an avg of 15 tabs, Two Servers on two terminals , Spotify, Telegram, iMessage App, Email App and some other did bits mainly on the laptop. 16gb RAM, core i7 2.3ghz.


Discussion
What's your opinion on hyper-threading and what are your views especially on the zombieload attack and performance gains/loss ?

truthCoder:
CAVEAT: I am not responsible for any data loss, device malfunction, divorce, flood, job loss, penile retraction or any other event that might happen as a result of embarking on this quest. I advise you conduct proper research on the subject before taking any steps on your computer

Hyper-threading is Intel's proprietary simultaneous multithreading (SMT) implementation used to improve parallelization of computations (doing multiple tasks at once) performed on x86 microprocessors. (Definition from Wikipedia)

For each physical core on your CPU's processor, the operating system addresses two virtual cores and shares the workload between them when possible.

In layman terms, assuming your CPU is a bus with 4 seats, Intel's conductor puts two passengers on each seat so the bus can transport 8 passengers at once. The bus performs like an 8 passenger vehicle when it is actually a 4 passenger vehicle.

A processor might be able to perform 4 arithmetic operations every clock cycle, yet be limited to 2 operations per cycle by nature of the running program. This would leave 2 idle “slots”, which wastes performance. Hyperthreading attempts to fill these slots by running another program at the same time. (I culled this part from an answer on Quora)

Hyper-threading works on the basis that there would be stall times where the cores are idle and tries to maximise efficiency by adding extra threads when possible. Continuing with the analogy, the conductor checks each passenger boarding and tells the slim ones to lap each other. The ones with big bodies are allowed to seat alone.

Many apps can benefit from hyper-threading as it increases relative performance, ceteris paribus.

Why you should Turn It Off.

Battery Drain:
There is no free lunch in Freetown. Running your cores at double their capacity implies consuming more power. If you are on a battery powered laptop, this could reach as much as 30% power savings if hyper-threading is disabled.

Temperature:
When a CPU draws more power, it is converted into heat. This makes your computer get hotter and unbearable to lap. Heat savings from disabling hyper-threading can be up to 10C or more.

Gaming
Many games actually benefit from disabling hyper threading. Many gamers have reported increased performance after their hyperthreading has been disabled. This is because hyper threading was designed to maximise efficiency on small and short computes but games do not follow this pattern.

ZombieLoad Attack:
There is an exploit on all intel cpus called the zombieload attack. This attack exploits the core of hyper-threading which combines different processes onto same core and allows data access by an attacker. No matter how strong your encryption keys or operating system is, it could be exploited at the CPU level. All major OS has been tested and they all fail in this regards. It is even possible to read Tor encryptions by an attacker using ZombieLoad. The solution offered has been to disable hyper-threading. It is recommended to update your OS with the latest security updates prior.

Disabling Hyper-Threading
Each OS / Device Manufacturer has its own process for disabling hyper-threading and I would advise you consult on this before proceeding.
Follow the official recommended process available on the manufacturer's website. To begin, you can google "How to disable hyper-threading on Bleep" where Bleep is your device name, model and OS.

Discussions on Performance Loss
Intel has stated that a 7% loss in performance should be expected from disabling hyperthreading. Apple was been conservative and said a loss of up to 40% should be expected. This has been discounted by various testers and many people. The intel figures are more realistic from tests conducted in recent studies.

My Own Experience
I disabled hyper threading on a 2012 MacBook Pro, Catalina 10.15.7, (latest security update added) after following Apple's official recommendation and have the result below:
Average: CPU Temp. dropped 10C. I can now easily put my laptop on my bare laps as I work on the bed.
Battery: I have gained more than an extra hour of battery use.
Responsiveness: The laptop does is still very responsive. I have no stuttering issues
Noticeable drawback: To start the laptop, I have to long-press the power button for a few seconds instead of the previous touch and go. Since I hardly shut down my MacBook Pro, this is not an issue. (I usually go many weeks without shutting down the laptop.)


Discussion
What's your opinion on hyper-threading and what are your views especially on the zombieload attack and performance gains/loss ?

Can you facilitate (mentor) peeps on some special computer courses like this hyper threading and it's likes.?

truthCoder:


My core is on Web dev. via the JAMStack approach. My passion is on Svelte and Svelte-Kit as interesting alternatives to the ReactJs School of Bandwagonry and Verbose studies.

I can do research on differing subjects and analyse different approaches to come up with a clear and defined solution to complex looking problems. This does not make me an expert on those subjects. I do not claim to be an expert on anything whatsoever (apart from grilling chicken and eating it with two cold bottles of Guinness Stout).

If you don't mind someone as dumb as me, then why not.

I see...howbeit some of the spellings make your reply not too comprehendeable...can you kindly correctly edit it.

@Seniorwriter

Seniorwriter:


Can you facilitate (mentor) peeps on some special computer courses like this hyper threading and it's likes.?

@Seniorwriter

My core is on Web dev. via the JAMStack approach. My passion is on Svelte and Svelte-Kit as interesting alternatives to the ReactJs School of Bandwagonry and Verbose studies.

I can do research on differing subjects and analyse different approaches to come up with a clear and defined solution to complex looking problems. This does not make me an expert on those subjects. I do not claim to be an expert on anything whatsoever (apart from grilling chicken and eating it with two cold bottles of Guinness Stout).

If you don't mind someone as dumb as me, then why not.

Seniorwriter:


Can you facilitate (mentor) peeps on some special computer courses like this hyper threading and it's likes.?

I see...howbeit some of the spellings make your reply not too comprehendeable...can you kindly correctly edit it.

@Seniorwriter

Can you please point to the spellings you noticed that made my response not comprehendible?