Intel and Microsoft have insisted that the performance impact of the Kernel Page Table Isolation fix for the recently-revealed Meltdown vulnerability will be much smaller than people feared. Now, Intel's released some hard numbers, and perhaps to the consternation of the "everything is 30% slower" doomsayers, the actual impact for client users on modern machines appears to be minimal.
Intel's testing was done using Skylake, Kaby Lake, and Coffee Lake CPUs on Windows 10, as well as Skylake machines running Windows 7. All of the test rigs were equipped with SSDs, although Intel also tested the Skylake-and-Windows-7 combo on a hard-drive-based system. The company put the machines through SYSmark 2014 SE, PCMark 10, 3DMark Sky Diver, and WebXPRT 2015 both before and after the vulnerability mitigation patches. The chart that Intel published presents results as percentages of relative performance compared to the pre-patch systems.
Ultimately the results trend close to the 5% mark overall. Many tests, particularly 3DMark, show a 1-2% difference or none at all. The worst-case scenario appears to be SYSMark 2014's Responsiveness test which sees double-digit performance hits on every platform except the Windows 7 setup with a hard drive (which actually sees a performance gain). WebXPRT 2015 also sees slowdowns in the 5-10% range, but otherwise the differences are pretty minimal.
The published results summarize the speed hit that client users on recent platforms are likely to see. Intel says it plans to prepare a "representative" data set of results for hardware released within the last five years that should likely cover most active systems in the field today. Other reports have placed the performance impact for big servers and datacenters much higher, though. For now, you can click here and see Intel's chart for yourself.