GIMP is one of the real-world programs seeing a measurable slowdown in performance with Linux 4.15 due to KPTI/Retpoline.

The synthetic socket activity benchmark from Stress-NG also shows its performance hit on both systems from Spectre v2 and Meltdown mitigation.

The context switching performance hit is also evident.

On both systems, the Apache web server performance has gradually gotten slower with the newer kernel releases.

Hackbench is another kernel benchmark showing the performance impact on Linux 4.15.

Overall on both of these systems we find Linux 4.15 to take a performance hit in workloads dealing with a lot of kernel interactions, but at least in some instances the lower performance is still ahead of where the performance was on much older kernel releases. Thankfully though some performance optimizations are in the works that may hit for the upcoming Linux 4.16 merge window. Once the Linux 4.16 development begins to settle down, stay tuned for results being added in to these system metrics along with plenty of other benchmarks on Phoronix.