Several days ago we've noticed that our Jenkins master had almost all its 12 core under 100% load. Apparently it's been that way for several days straight. Using Monitoring plugin we've figured out there was about 10 threads with tremendous amount of time spent in `java.util.TreeMap.put`. Killing those threads one by one didn't break anything, so we assumed it to be some strange jenkins quirk and went on. AFAIK stack traces weren't informative.

Today I noticed there are 3 threads each eating 100% of core again. This time stack traces are more informative (see attachments). I cannot confirm that those two issues with CPU load are directly correlated, but the current one seems legit enough.