How To Disable CPU Hyperthreading to Improve Performance

Hyperthreading is an Intel technology that allows a single physical CPU core to act as two logical cores by splitting each core into two virtual cores. The goal is to maximize CPU efficiency by keeping execution units in the CPU busy during potential lulls in processing.

## What is Hyperthreading and How Does it Work?

Hyperthreading works by duplicating certain sections of the processor, including the architectural state, so that additional threads can run simultaneously. From the operating system’s perspective, a hyperthreaded core appears as two processors instead of one. This allows the operating system to schedule two threads or processes simultaneously on one core.

The technology takes advantage of the fact that modern processors often spend time waiting for data from memory or disk. By running another thread in parallel, the CPU can avoid wasting those cycles where it would otherwise be forced to sit idle.

So while hyperthreading does not literally double the computing power, it can lead to performance improvements, especially for multi-threaded workloads.

## When Does Hyperthreading Help Performance?

Hyperthreading tends to provide the biggest performance boosts in the following situations:

  • Multi-threaded applications, especially highly parallelized tasks like media encoding, file compression, simulations, neural networks, etc.
  • Servers running many simultaneous threads and processes
  • Multitasking environments where many background tasks are running

Applications specifically optimized for multi-threading see the largest gains from hyperthreading. The technology allows more threads to run concurrently, facilitating faster overall execution.

## When Can Disabling Hyperthreading Improve Performance?

While hyperthreading can maximize CPU utilization in many instances, there are some cases where disabling it may provide a performance advantage:

Applications Not Optimized for Multi-Threading

Some software is not designed to take advantage of multiple threads. Legacy applications in particular may perform worse with hyperthreading enabled. The simultaneous threads end up competing for shared resources, hampering performance. Disabling hyperthreading allows the single thread to maximize use of the available resources.

Avoiding Thread Contention in Games

For games, hyperthreading can sometimes cause worse performance due to thread contention. If a game inadvertently schedules threads poorly across physical and logical cores, it can lead to contention where the threads are constantly interrupting each other and fighting for resources. Disabling hyperthreading may improve stability and achieve higher frame rates.

Reducing Heat Output

Hyperthreading requires duplicated processor resources and keeping more of the CPU active. This in turn can lead to higher thermals as the CPU works harder to handle the extra threads. For thermally constrained systems like laptops, disabling hyperthreading may lower temperatures.

Security Concerns

Some speculation-based security vulnerabilities like Spectre and Meltdown received partial mitigations by disabling hyperthreading. For highly security-focused environments, the tradeoff in safety may justify the performance loss.

## How to Disable Hyperthreading

The process for disabling hyperthreading will vary slightly depending on your CPU and motherboard:

  1. Reboot your computer and enter the BIOS setup utility. The key to press varies – common options include Delete, F1, F2, F10 or F12.
  2. Navigate to the configuration menu for your processor settings. For Intel systems, look for an option labelled “Hyperthreading” or something similar.
  3. Change the hyperthreading toggle from enabled to disabled.
  4. Save changes and exit BIOS. Reboot computer to apply new settings.

Alternatively, hyperthreading can be disabled within the operating system using utilities that modify CPU affinity, restricting logical processors. However, BIOS method prevents enabling again accidentally.

## Performance Differences With Hyperthreading On vs Off

Whether disabling hyperthreading boosts or reduces performance depends heavily on your workload. Testing with real applications is the only reliable way to determine the right setting.

That said, some general observations when disabling hyperthreading:

  • Single-threaded tasks will run at similar speeds either way.
  • Multi-threaded productivity apps may see a 10-30% slowdown.
  • Servers with high concurrent users can experience more severe performance hits.
  • Games are a mixed bag. Some see gains, others losses.
  • CPU rendering and encoding will nearly always be slower without hyperthreading.

If your use case does not involve heavy multi-tasking, try disabling hyperthreading and benchmarking to see if it helps or hinders. Just don’t prematurely disable it without testing first.

## Conclusion

Hyperthreading can accelerate multi-threaded workloads by keeping the CPU cores busier. But occasionally single threads still need full access to the core resources without interference.

By disabling hyperthreading in scenarios with thread contention, it prevents logical cores from stepping on each other. This avoids hindered performance from fighting over shared registers and execution units in the processor.

Always measure your particular applications before and after changing the setting. Hyperthreading has tradeoffs, and the results really depend on the environment and programs utilized. But when utilized properly, it remains an innovative way to boost CPU parallelization.