1.8 pre1 server crash

Running a 1.8-pre1 server, is extremely demanding on the server computer I have running, uses between 70 and 100% of the cpu usage, whereas the 1.7.10 server uses between 10 and 50% of the cpu usage. I keep getting "[19:53:53] [Server thread/WARN]: Can't keep up! Did the system time change, or is the server overloaded? Running 47485ms behind, skipping 949 tick(s)" errors and crashes like the one attached when doing things like generating new world chunks. Mob and player movement seems to skip as if I had connection lag, but i'm inside the network of the server.