The patches related to the mitigation of meltdown and spectre attacks, have they caused significant and noticeable slow down of execution in systems they have been applied to?
The full impact isn't known yet. It is also going to differ massively based on workload - code invoking large numbers of system calls is likely to invoke a notable hit whilst any difference to code mostly operating in user mode is unlikely to be measurable.
- Epic Games has already blamed the patches for service outages.
- Some artificial benchmarks have shown drops as drastic as 50%.
- Intel initially put out predictions of 5-7%.
- Toms Hardware have found no difference outside margin of error on a storage based test (Storage is one workload expected to be hit hardest).
There are not that many results, but for example Epic Games released a blog post that shows doubled CPU load on one of there cloud servers after installing the Meltdown mitigation. This is definitely significant and noticeable. But the overhead depends heavily on the workload. If it is noticeable by you can only be found out by you after patching.