>So you’re saying that the latest RCS, without the patch, was supposed to be slower than stable by at least 10%? I'm saying that it's not a reliable measuremen

>So you’re saying that the latest RCS, without the patch, was supposed to be slower than stable by at least 10%? I'm saying that it's not a reliable measurement of the impact of the PTI patchset. There was a PgSQL performance anecdote [0] (actually tested with the real boot parameters instead of entirely different versions of the kernel) that showed 9% performance decrease posted to LKML, which Linus described as "pretty much in line with expectations". [1] Quoting further from that mail: > Something around 5% performance impact of the isolation is what people are looking at. > Obviously it depends on just exactly what you do. Some loads will hardly be affected at all, if they just spend all their time in user space. And if you do a lot of small system calls, you might see double-digit slowdowns. So in general, the hit should be around 5%, and "[y]ou might see double-digit slowdowns" seems like the hit on a worst-case workload is hovering closer to the 10% range than 30%. That's also what the anecdote from LKML shows, unlike Phoronix which shows 25%-30% or worse. This is more of an attrition thing than a staggering loss. With people saying MS patched this in November, it would be interesting to see if people saw a similar 5-10% degradation in Windows benchmarks since that time. >How often do companies release performance downgrades of that scale? I don't know which "company" you're referring to here, but substantial changes in kernel performance characteristics are pretty common during the Linux development/RC process, and yes, definitely some workloads will often see changes +/- 10% between the roughly bi-monthly stable kernel releases. If you're surprised that Linux development is so "lively", you're not alone. That's one of the selling points of other OSes like FreeBSD. [0] https://lkml.org/lkml/2018/1/2/678 https://lkml.org/lkml/2018/1/2/678 [1] https://lkml.org/lkml/2018/1/2/703 https://lkml.org/lkml/2018/1/2/703