Microsoft Details Performance Impact of Spectre & Meltdown Mitigations On Windows Systems…. And You Won’t Like Them

In case you were wondering how fixes for Spectre and Meltdown will affect you from a speed perspective, Microsoft has done the work for you to find out. Delivering the news is Microsoft’s Windows chief Terry Myerson via this blog post:

With Windows 10 on newer silicon (2016-era PCs with Skylake, Kabylake or newer CPU), benchmarks show single-digit slowdowns, but we don’t expect most users to notice a change because these percentages are reflected in milliseconds.

With Windows 10 on older silicon (2015-era PCs with Haswell or older CPU), some benchmarks show more significant slowdowns, and we expect that some users will notice a decrease in system performance. With Windows 8 and Windows 7 on older silicon (2015-era PCs with Haswell or older CPU), we expect most users to notice a decrease in system performance.

Windows Server on any silicon, especially in any IO-intensive application, shows a more significant performance impact when you enable the mitigations to isolate untrusted code within a Windows Server instance. This is why you want to be careful to evaluate the risk of untrusted code for each Windows Server instance, and balance the security versus performance tradeoff for your environment.

For context, on newer CPUs such as on Skylake and beyond, Intel has refined the instructions used to disable branch speculation to be more specific to indirect branches, reducing the overall performance penalty of the Spectre mitigation. Older versions of Windows have a larger performance impact because Windows 7 and Windows 8 have more user-kernel transitions because of legacy design decisions, such as all font rendering taking place in the kernel.

Take home message, if you’re PC is recent, it’s a non-issue. If it’s older, it sucks to be you. And if you’re running Windows Server, well…. You’re taking a hit no matter what CPU you have and it truly sucks to be you. This is one of the reasons why this CPU bug from Intel, AMD, and ARM is a big bloody deal. Because while the security implications are extremely problematic, the cure for them may be worse than the disease.

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