Expand description
Multicore Round-robin Scheduling.
In this part, you will implement round robin scheduler. Round robin is a scheduler that assigns equal amount of time slice into threads in circular order. When time slice is expired, the scheduler kicks out the thread from the running state and push back to the scheduling queue.
Background
Thread is an abstraction of a cpu core. Through the thread abstraction, the operating system can run multiple tasks on a cpu core.
KeOS already implemented some thread functionalities like thread creation,
thread switching.
You can create a new thread with ThreadBuilder. You provide a function to be run on
the thread as an argument to ThreadBuilder::spawn.
When the first time the thread runs, the function executed.
When the function is terminated, the thread also be terminated.
Each thread, therefore, acts like a mini-program running inside the kernel.
At any given time, exactly one thread runs and the rest, if any, become inactive.
The scheduler decides which thread to run next by calling Scheduler::next_to_run.
If no thread is ready to run at any given time, then the special idle thread runs.
The magics of a context switch lies on Thread::run. It saves the state of the
currently running thread and restores the state of the thread we’re switching to.
IMPORTANT NOTES
In KeOS, each thread is assigned a STACK_SIZE-size execution stack. The KeOS try to detect
the stack overflow, however it is not perfect. If the stack is overflowed, you can encounter a
mysterious kernel panics.
To prevent the such situation, DO NOT DECLARE large data structures (e.g. let v: [u8; 0x200000];)
and allocate them on heap through Box.
Implementation requirements
In this projects, you implements a round robin scheduler with 5ms time slices.
Note that Scheduler::timer_tick is called at every 1ms on each cpu.
When a new thread is reached, it must be pushed back to the current scheduling queue.
You are required to implement passive job stealing; when there is no task in the current runqueue, then steal from the other.
Implementation Order
You will fill the Scheduler trait implementor for RoundRobin struct.
Fill the todo!()s of RoundRobin scheduler.
Read the documentation of Scheduler to understand what each member does.
The project is straightforward. You will meet several todo!()s during implementation,
and replace those todo!()s to your implementation.