diff --git a/crate/process/src/processor.rs b/crate/process/src/processor.rs
index 9083dad..7db17f6 100644
--- a/crate/process/src/processor.rs
+++ b/crate/process/src/processor.rs
@@ -33,8 +33,6 @@ pub struct Processor_<T: Context, S: Scheduler> {
     procs: BTreeMap<Pid, Process<T>>,
     current_pid: Pid,
     event_hub: EventHub<Event>,
-    /// Choose what on next schedule ?
-    next: Option<Pid>,
     // WARNING: if MAX_PROCESS_NUM is too large, will cause stack overflow
     scheduler: S,
 }
@@ -65,7 +63,6 @@ impl<T: Context, S: Scheduler> Processor_<T, S> {
             },
             current_pid: 0,
             event_hub: EventHub::new(),
-            next: None,
             scheduler,
         }
     }
@@ -74,7 +71,7 @@ impl<T: Context, S: Scheduler> Processor_<T, S> {
         self.scheduler.set_priority(self.current_pid, priority);
     }
 
-    pub fn set_reschedule(&mut self) {
+    pub fn yield_now(&mut self) {
         let pid = self.current_pid;
         self.set_status(pid, Status::Ready);
     }
@@ -108,7 +105,7 @@ impl<T: Context, S: Scheduler> Processor_<T, S> {
     pub fn tick(&mut self) {
         let current_pid = self.current_pid;
         if self.scheduler.tick(current_pid) {
-            self.set_reschedule();
+            self.yield_now();
         }
         self.event_hub.tick();
         while let Some(event) = self.event_hub.pop() {
@@ -116,12 +113,12 @@ impl<T: Context, S: Scheduler> Processor_<T, S> {
             match event {
                 Event::Schedule => {
                     self.event_hub.push(10, Event::Schedule);
-                    self.set_reschedule();
+                    self.yield_now();
                 },
                 Event::Wakeup(pid) => {
                     self.set_status(pid, Status::Ready);
-                    self.set_reschedule();
-                    self.next = Some(pid);
+                    self.yield_now();
+                    self.scheduler.move_to_head(pid);
                 },
             }
         }
@@ -150,13 +147,13 @@ impl<T: Context, S: Scheduler> Processor_<T, S> {
         if self.get(self.current_pid).status == Status::Running {
             return;
         }
-        let pid = self.next.take().unwrap_or_else(|| self.scheduler.select().unwrap());
+        let pid = self.scheduler.select().unwrap();
         self.switch_to(pid);
     }
 
-    /// Switch process to `pid`, switch page table if necessary.
-    /// Store `rsp` and point it to target kernel stack.
+    /// Switch to process `pid`.
     /// The current status must be set before, and not be `Running`.
+    /// The target status must be `Ready`.
     fn switch_to(&mut self, pid: Pid) {
         // for debug print
         let pid0 = self.current_pid;
@@ -203,7 +200,7 @@ impl<T: Context, S: Scheduler> Processor_<T, S> {
         if let Some(waiter) = self.find_waiter(pid) {
             info!("  then wakeup {}", waiter);
             self.set_status(waiter, Status::Ready);
-            self.next = Some(waiter);
+            self.scheduler.move_to_head(waiter);
         }
     }
 
diff --git a/crate/process/src/scheduler.rs b/crate/process/src/scheduler.rs
index 4d8e696..9ab52fa 100644
--- a/crate/process/src/scheduler.rs
+++ b/crate/process/src/scheduler.rs
@@ -9,6 +9,7 @@ pub trait Scheduler {
     fn select(&mut self) -> Option<Pid>;
     fn tick(&mut self, current: Pid) -> bool;   // need reschedule?
     fn set_priority(&mut self, pid: Pid, priority: u8);
+    fn move_to_head(&mut self, pid: Pid);
 }
 
 pub use self::rr::RRScheduler;
@@ -79,6 +80,14 @@ mod rr {
 
         fn set_priority(&mut self, pid: usize, priority: u8) {
         }
+
+        fn move_to_head(&mut self, pid: usize) {
+            let pid = pid + 1;
+            assert!(self.infos[pid].present);
+            self._list_remove(pid);
+            self._list_add_after(pid, 0);
+            trace!("rr move_to_head {}", pid - 1);
+        }
     }
 
     impl RRScheduler {
@@ -95,6 +104,10 @@ mod rr {
             self.infos[prev].next = i;
             self.infos[at].prev = i;
         }
+        fn _list_add_after(&mut self, i: Pid, at: Pid) {
+            let next = self.infos[at].next;
+            self._list_add_before(i, next);
+        }
         fn _list_remove(&mut self, i: Pid) {
             let next = self.infos[i].next;
             let prev = self.infos[i].prev;
@@ -156,13 +169,17 @@ mod stride {
             let info = &mut self.infos[pid];
             assert!(info.present);
             info.present = false;
-            // BinaryHeap only support pop the top.
-            // So in order to remove an arbitrary element,
-            // we have to take all elements into a Vec,
-            // then push the rest back.
-            let rest: Vec<_> = self.queue.drain().filter(|&p| p.1 != pid).collect();
-            use core::iter::FromIterator;
-            self.queue = BinaryHeap::from_iter(rest.into_iter());
+            if self.queue.peek().is_some() && self.queue.peek().unwrap().1 == pid {
+                self.queue.pop();
+            } else {
+                // BinaryHeap only support pop the top.
+                // So in order to remove an arbitrary element,
+                // we have to take all elements into a Vec,
+                // then push the rest back.
+                let rest: Vec<_> = self.queue.drain().filter(|&p| p.1 != pid).collect();
+                use core::iter::FromIterator;
+                self.queue = BinaryHeap::from_iter(rest.into_iter());
+            }
             trace!("stride remove {}", pid);
         }
 
@@ -195,6 +212,15 @@ mod stride {
             self.infos[pid].priority = priority;
             trace!("stride {} priority = {}", pid, priority);
         }
+
+        fn move_to_head(&mut self, pid: Pid) {
+            if self.queue.peek().is_some() {
+                let stride = -self.queue.peek().unwrap().0;
+                self.remove(pid);
+                self.infos[pid].stride = stride;
+                self.insert(pid);
+            }
+        }
     }
 
     impl StrideScheduler {
diff --git a/crate/process/src/thread.rs b/crate/process/src/thread.rs
index 1a93dd8..8786cc8 100644
--- a/crate/process/src/thread.rs
+++ b/crate/process/src/thread.rs
@@ -107,7 +107,7 @@ impl<S: ThreadSupport> ThreadMod<S> {
     pub fn yield_now() {
         info!("yield:");
         let mut processor = S::processor();
-        processor.set_reschedule();
+        processor.yield_now();
         processor.schedule();
     }