Upon further reflection, I think it does not make sense for application programmer to control CPU distribution down to the ticks.
This would over-specify the scheduling requirements, which often are quite lax.
Presence of multiple physical processors makes the situation even worse.
What probably makes sense is to allow the application developer to explicitly track the separate computation parts, assigning to them various properties, and enabling two-way reflective link between the programmer and the real scheduler.
Think of this as a task management system, e.g., Jira.
Persons acting in one role can create tasks, manage their dependencies, deadlines, estimates and priorities, while persons in another role execute the project making sure the tasks are completed at a satisfactory time.
The first role is like one for the application developer, the second one is for the scheduler of the language's runtime.