February 12, 2018

KPTI/KAISER Meltdown Initial Performance Regressions

The recently revealed Meltdown and Spectre bugs are not just extraordinary issues of security, but also performance. The patches that workaround Meltdown introduce the largest kernel performance regressions I've ever seen. Many thanks to the engineers working hard to develop workarounds to these processor bugs.

In this post I'll look at the Linux kernel page table isolation (KPTI) patches that workaround Meltdown: what overheads to expect, and ways to tune them. Much of my testing was on Linux 4.14.11 and 4.14.12 a month ago, before we deployed in production. Some older kernels have the KAISER patches for Meltdown, and so far the performance overheads look similar. These results aren't final, since more changes are still being developed, such as for Spectre.

Note that there are potentially four layers of overhead for Meltdown/Spectre, this is just one. They are:

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