20% when running SELECT 1; over a loopback network interface, not in real-world workloads.

The other benchmark that has generated some consternation is running 'du' on a nonstop loop.

Both of these situations are pathological cases and don't reflect real-world performance. My guess is a 5-10% performance hit on general workloads. Still significant, but nowhere near as bad as some of the numbers that are getting thrown around.

And, databases are the worst case scenario, most real-world applications are showing 1% performance impact or less.

https://www.computerbase.de/2018-01/intel-cpu-pti-sicherheit...

https://www.hardwareluxx.de/index.php/news/hardware/prozesso...

Another quick postgres estimate [1] with lower impact and a a reply from Linus Torvalds that this values are in the range what they are expecting from the patch. "... Something around 5% performance impact of the isolation is what people are looking at. ..." [2]

[1] http://lkml.iu.edu/hypermail/linux/kernel/1801.0/01274.html [2] http://lkml.iu.edu/hypermail/linux/kernel/1801.0/01299.html