Are you seeing 50% in Task Manager for the WCG xxxxx processes, each? In Windows when it shows 50% of 1 task on a Duo is equal 100% (or whatever cycle% is spare) of 1 core.... on Linux 100% is shown if 100% is used of 1 core.

Anyway to clarify, do you want BOINC to use only a portion (1/2) of the CPU cores or do you want it to use 50% 'per' core, e.g. to lower the operating temperature, which is controlled with the "Use at most 100% CPU time"? If you see only 1 task running in Tasks Manager and in BOINC tasks view then you've already achieved your goal.

Of course, the activity menu setting needs setting to "Run based on preferences", as else BOINC with Run Always and will go 100% full out. BUT, in experimenting, the number of cores/% entered is what BOINC uses regardless if running based on preferences. Only the % time is influenced by this option. I've also experimented with the % of processor to less than 50% on the duo. BOINC will then ignore and use the minimum possible i.e. 10% will still use 50% of the cores on a duo.

Let us know.

I have the wcg task which is at 50% all the time and the idl task to 50%.

I would like to have the wcg task at 25% all the time, because the fan run too fast.

But as you said the only way is to have Use at most 50% CPU time and On multiprocessor systems, use at most 50% of the processors.

I will have 50% of 50% = 25%.
Thanks a lot for you help.

Wilgard