Again, I reiterate, because this is important! Previously I’ve linked to an article about Linus Torvalds agreeing that Linux is bloated, but that was a few years ago. Well, we’re still at the progressive slowing down of the Linux kernel. Here is yet another newer article on the same subject. But, some of the specifics rae different. In light of the Meltdown and Spectre bugs, some of the mitigations have resulted in notable slowdowns, but these are not the result of the largest slowdowns. The largest slowdowns were due to configuration errors, some introduced by newer changes, others introduced simply by inability to auto-configure with newer hardware.
Companies like Red Hat and Google spend 6-12 months tuning the kernel, but Linux kernel releases come out every 2-3 months. Google uses a team of 100 engineers to do this.
20191109/https://blog.acolyer.org/2019/11/04/an-analysis-of-performance-evolution-of-linuxs-core-operations/