Put the CPU to sleep when no task is ready

src/task/executor.rs

@@ -32,6 +32,7 @@ impl Executor {
         loop {
             self.wake_tasks();
             self.run_ready_tasks();
+            self.sleep_if_idle();
         }
     }
 
@@ -65,6 +66,22 @@ impl Executor {
         }
     }
 
+    fn sleep_if_idle(&self) {
+        use x86_64::instructions::interrupts::{self, enable_interrupts_and_hlt};
+
+        // fast path
+        if !self.wake_queue.is_empty() {
+            return;
+        }
+
+        interrupts::disable();
+        if self.wake_queue.is_empty() {
+            enable_interrupts_and_hlt();
+        } else {
+            interrupts::enable();
+        }
+    }
+
     fn create_waker(&self, task_id: TaskId) -> Waker {
         Waker::from(Arc::new(TaskWaker {
             task_id,