diff --git a/kernel/src/scheduler.rs b/kernel/src/scheduler.rs
index 97b342f..13c9b9c 100644
--- a/kernel/src/scheduler.rs
+++ b/kernel/src/scheduler.rs
@@ -1,6 +1,6 @@
 use crate::objects::*;
 use core::ptr::NonNull;
-use log::error;
+use log::{error, trace};
 use spin::lazy::Lazy;
 use utils::linked_list::Link;
 
@@ -40,19 +40,18 @@ impl Scheduler {
 
     pub fn schedule(&self) {
         while let Some(next) = self.head.next_mut() {
-            // TODO: also need to check whether it is schedulable
-            if next.timetick() > 0 {
-                // Available to run, activate it
+            if next.timetick() > 0 && next.schedulable() {
+                trace!("[Scheduler] Switch to {}, tick: {}", next.tid(), next.timetick());
                 next.activate();
             } else if next.timetick() == 0 {
-                // No time left, refill time tick and move to the end of the queue
                 next.set_timetick(TIME_SLICE);
             }
 
             // put to the end of the queue
-            // todo: only move blocked and time expired threads to the end
-            next.link.detach();
-            self.head.prepend(next);
+            if next.timetick() == 0 || !next.schedulable() {
+                next.link.detach();
+                self.head.prepend(next);
+            }
         }
 
         error!("[Scheduler] No thread to schedule! Where is IDLE thread?");