It’s rare that a security vulnerability affects a huge swath of processors all at once, but the Spectre vulnerabilities that were uncovered in 2018 were so widespread that they forced operating system vendors to trade performance for protection. Windows started carrying mitigations to protect against it that were on by default, and it did take sacrificing some CPU performance. They’re still enabled by default today, and users can switch it off if they please with a simple registry tweak. Whether doing so is a smart optimization measure or just an unnecessary risk depends on what the machine is used for and the age of the CPU, and the latter matters a lot more than it used to.
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The Spectre mitigations are still active
A family of attack vectors on speculative execution
Spectre is a family of different attacks on the same processor technique called speculative execution, which is used in virtually every modern CPU. Processors use this technique to stay fast by guessing ahead as to where the code will go, and discarding the incorrect guesses. Traces of those incorrect guesses linger in the cache, and with a carefully written program, someone could feasibly infer sensitive data based on those traces. The variant that takes advantage of that mechansim is the Spectre variant 2, or branch target injection, where an attacker trains the CPU’s branch predictor to steer the speculation somewhere useful for them, such as into the kernel code that handles secrets.
The mitigations that Windows put in place restricts that kind of speculation that happens at the boundary between apps and the kernel, and that’s where the performance cost lies. It’s not a throttle as much as it is just a bit of extra work that happens every time a program hands something off to the OS. Workloads that cross a lot of boundaries of the system often, like storage and code compiling, feel this a lot more. Anything that runs solely on the CPU cores themselves and doesn’t call into the kernel won’t really notice a performance impact.
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The performance cost can be real
Microsoft admitted that it can have a significant impact
When Microsoft shipped these mitigations in 2018, it released them along with their own testing, which showed single-digit slowdowns on WIndows 10 PCs with Skylake or newer Intel processors. On Haswell and older, some benchmarks showed larger drops that users would definitely feel a bit more. Microsoft also noted that the first Spectre variant and Meltdown could be patched without significant slowdowns, which left variant 2 as the expensive one to patch as far as performance went.
The registry value FeatureSettingsOverride controls which OS-side mitigations are turned on, and there are some free utilities out there that you can use to turn these off without regedit along with others, such as the mitigations for Meltdown. If you were to change the registry value to the value most commonly shared online, 3, you would disable Meltdown protection as well, while a value of 1 turns off only the Spectre variant 2 mitigation. Either way, the change affects only the operating system’s side of the defense.
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Newer CPUs don’t benefit as much
The newer you get, the less you gain from turning off Spectre mitigations
Newer chips fix some of these flaws directly in silicon and make the rest cheaper to mitigate, and Windows itself moved to lower-overhead mitigation techniques like retpoline back in 2019. On a recent Ryzen or Intel processor, disabling the mitigation in the OS probably won’t give you any measurable performance increase. The risk of doing so also isn’t purely theoretical, either. In 2021, researcher Julien Voisin found working Spectre exploits for Windows and Linux uploaded to VirusTotal. They were traced back to Immunity’s commercial penetration-testing platform, Canvas. Later, in 2024, researchers at Vrije Universiteit Amsterdam demonstrated an attack called Native BHI that leaked kernel memory on Intel systems running Linux despite the protections already being in place, and Microsoft has continued publishing guidance for newer variants.
Of course, for these types of exploits, malicious code has to exist and be actively running on the machine, so something that exclusively plays games or lives in the living room as a media box isn’t really at risk for these types of exploits. Turning off Spectre might not net you a terrible amount of performance, but Microsoft does point to Memory Integrity and the Virtual Machine Platform as features that can hurt performance in specific scenarios, though turning those off comes with their own set of potential security trade-offs.
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Spectre mitigations are there for a reason
While disabling Spectre mitigations to increase performance isn’t a complete myth, they’re not nearly as effective as the used to be. On a decade-old processor, it can return real performance to workloads that lean on the kernel and cross between different components on the system, but on a modern CPU, it trades away protection for a few benchmark points. Whether that’s worth it for you will come down to your specific system and workload.