Context switches slower in new Linux kernels

Linux vDSO maintainer here:

1. Don't use RDTSC manually. On many CPUs it produces flat-out wrong results. Use clock_gettime with either CLOCK_REALTIME or CLOCK_MONOTONIC depending on what you're trying to do. It's barely slower than a correctly ordered RDTSC. (You remembered to read the SDM/APM carefully and noticed that RDTSC is executed speculatively and doesn't time what you think it does, right?)

2. Don't tune C states in firmware. Use intel_idle's tuning. It's much more reliable.

3. You think that idle=mwait triggers C1E directly and that's a good thing? Hah! The BIOS setting that's usually described as "[gobbledygook] C1E [more gibberish]" is actually C1E Auto-Promotion, which is a truly awful feature that will detect, in hardware (or really power control firmware) when all cores are in C1 or deeper and promote it to a really deep package state that can take tens of milliseconds to wake from. That's right: it detects when the OS said it wanted a light sleep (C1) for low wakeup latency and promotes it to a very deep sleep. This is bad enough that the excellent intel_idle driver automatically turns it off.

Why did this get knocked of the main-page? Is stackoverflow a penalized url now ?

This is from 2012: is it still relevant?

Question for @dang and @nick: for links to SO questions, is it possible to automatically date them if they aren't the current year?

Very interesting.. will have to do some local benchmarking. At the very least, the linked google C-state utility is a new addition to my admin toolkit.