L2J Server CPU Problem

[Forgiven20]

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Server specs : Intel i7 2600k 8 cores, 12GB RAM , 1 SSD 120 , 1 HDD 1 TB / OS : Linux x64/Windows x64

Hey guys,

I'm working at 1 server L2J Interlude on Windows x64 and Linux x64 doing a lot of tests.
As I saw on forum already 1 post with CPU Overload problems near to be same like me but without an answer to solve this problem.
So the problem I need help to get fixed is the CPU Usage of Java.
I really don't know why if I have 0 players my CPU stays 30% usage.
To explain detailed :
I start server CPU usage is 1-2%.
After 1 player online game the CPU goes 20-30% after he log out the CPU maintain the 20-30 Usage.
So it's normal ? I test this on Linux x64 and Windows x64 and of course I use java jdk x64 and same problem.
I was thinking example : If I open my server for live with 1000 players online what will happen with my CPU Oo 100% usage and temperature ??? = crash?
If you have any advice how can I fix this real problem please don't hesitate to write.
Thank you.

Regards,
Alecs