Microsoft Confirms Performance Decrease on Older Windows Versions

A Microsoft official confirmed today that some devices running on older Windows versions will see a significant slowdown and decrease in system performance after applying the Meltdown and Spectre security patches.

More precisely, this is how Meltdown and Spectre patches are going to affect Microsoft's products, as detailed today by Terry Myerson, Executive Vice President of the Windows and Devices Group.

  • 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," Myerson said.

"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," the Microsoft exec added.

Many saw the slowdowns coming

The slowdowns were to be expected due to the nature of the bugs and the type of patching required to get them fixed. Many described the Meltdown and Spectre vulnerabilities as flaws in the basic design of modern processors, so the patches were expected to cause problems.

Intel said its processors would be affected based on the type of operations the CPU would carry out, saying that syscall-heavy processes would suffer the most.

We knew Windows systems would be affected when a data scientist reported last week that Python now takes more to process the same data on a patched Windows 7 PC.

Similar slowdowns on Linux, AWS

Some of the Meltdown and Spectre mitigations introduced in the Linux kernel caused similar performance dips to the ones now disclosed by Microsoft.

Initial estimations said the Linux Meltdown and Spectre patches would produce between 5% and 50% slowdowns, but further tests and benchmarks proved many claims exaggerated. RedHat cut down the performance penalties on its systems to a range from 1% to 20%.

Over the course of last week, it became apparent that many companies were affected. EpicGames and BranchMetrics both reported issues after applying the Meltdown and Spectre patches.

Many companies should expect their AWS cloud computing bill to go up because it now takes more time to process the same amount of data.

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