diff --git a/crate/process/src/event_hub.rs b/crate/process/src/event_hub.rs
index f826cd0..97fa80c 100644
--- a/crate/process/src/event_hub.rs
+++ b/crate/process/src/event_hub.rs
@@ -1,4 +1,4 @@
-use alloc::collections::BinaryHeap;
+use alloc::collections::VecDeque;
 use core::cmp::{Ordering, PartialOrd};
 
 type Time = usize;
@@ -30,32 +30,63 @@ impl<T> Ord for Timer<T> {
 
 pub struct EventHub<T> {
     tick: Time,
-    timers: BinaryHeap<Timer<T>>,
+    timers: VecDeque<Timer<T>>,
 }
 
-impl<T> EventHub<T> {
+impl<T: PartialEq> EventHub<T> {
     pub fn new() -> Self {
         EventHub {
             tick: 0,
-            timers: BinaryHeap::new(),
+            timers: VecDeque::new(),
         }
     }
     pub fn tick(&mut self) {
         self.tick += 1;
     }
     pub fn pop(&mut self) -> Option<T> {
-        match self.timers.peek() {
+        match self.timers.front() {
             None => return None,
             Some(timer) if timer.time != self.tick => return None,
             _ => {}
         };
-        self.timers.pop().map(|t| t.data)
+        self.timers.pop_front().map(|t| t.data)
     }
     pub fn push(&mut self, time_after: Time, data: T) {
+        //debug!("{:?} {:?}", self.tick, time_after);
         let time = self.tick + time_after;
-        self.timers.push(Timer { time, data });
+        let timer = Timer { time, data };
+        let mut it = self.timers.iter();
+        let mut i : usize = 0;
+        loop {
+            let now = it.next();
+            if now == None {
+                break
+            };
+            if now.unwrap() < &timer {
+                break
+            };
+            i += 1;
+        }
+        self.timers.insert(i, timer);
     }
     pub fn get_time(&self) -> Time {
         self.tick
     }
+    pub fn remove(&mut self, data: T) {
+        let mut it = self.timers.iter();
+        let mut i : usize = 0;
+        loop {
+            let now = it.next();
+            if now == None {
+                break
+            };
+            if now.map(|t| &t.data).unwrap() == &data {
+                break
+            };
+            i += 1;
+        }
+        if i < self.timers.len() {
+            self.timers.remove(i);
+        }
+    }
 }
\ No newline at end of file
diff --git a/crate/process/src/process_manager.rs b/crate/process/src/process_manager.rs
index 2142ec3..b8931e7 100644
--- a/crate/process/src/process_manager.rs
+++ b/crate/process/src/process_manager.rs
@@ -26,10 +26,11 @@ pub enum Status {
     Exited(ExitCode),
 }
 
+#[derive(Eq, PartialEq)]
 enum Event {
     Wakeup(Pid),
+    Dropped,
 }
-
 pub trait Context {
     unsafe fn switch_to(&mut self, target: &mut Context);
 }
@@ -84,6 +85,7 @@ impl ProcessManager {
         while let Some(event) = event_hub.pop() {
             match event {
                 Event::Wakeup(pid) => self.set_status(pid, Status::Ready),
+                Event::Dropped => {},
             }
         }
         self.scheduler.lock().tick(pid)
@@ -126,20 +128,22 @@ impl ProcessManager {
     /// Switch the status of a process.
     /// Insert/Remove it to/from scheduler if necessary.
     fn set_status(&self, pid: Pid, status: Status) {
-        let mut scheduler = self.scheduler.lock();
         let mut proc_lock = self.procs[pid].lock();
         let mut proc = proc_lock.as_mut().expect("process not exist");
         trace!("process {} {:?} -> {:?}", pid, proc.status, status);
-        match (&proc.status, &status) {
-            (Status::Ready, Status::Ready) => return,
-            (Status::Ready, _) => scheduler.remove(pid),
-            (Status::Running(_), _) => {},
-            (Status::Exited(_), _) => panic!("can not set status for a exited process"),
-            (Status::Waiting(target), Status::Exited(_)) =>
-                self.wait_queue[*target].lock().retain(|&i| i != pid),
-            // TODO: Sleep -> Exited  Remove wakeup event.
-            (_, Status::Ready) => scheduler.insert(pid),
-            _ => {}
+        {   // limit the lifetime of scheduler
+            let mut scheduler = self.scheduler.lock();
+            match (&proc.status, &status) {
+                (Status::Ready, Status::Ready) => return,
+                (Status::Ready, _) => scheduler.remove(pid),
+                (Status::Running(_), _) => {},
+                (Status::Exited(_), _) => panic!("can not set status for a exited process"),
+                (Status::Waiting(target), Status::Exited(_)) =>
+                    self.wait_queue[*target].lock().retain(|&i| i != pid),
+                (Status::Sleeping, Status::Exited(_)) => self.event_hub.lock().remove(Event::Wakeup(pid)),
+                (_, Status::Ready) => scheduler.insert(pid),
+                _ => {}
+            }
         }
         match proc.status {
             Status::Running(_) => proc.status_after_stop = status,
@@ -165,8 +169,9 @@ impl ProcessManager {
         }
     }
 
-    pub fn sleep(&self, pid: Pid, time: usize) {
+    pub fn sleep(&self, pid: Pid, time_raw: usize) {
         self.set_status(pid, Status::Sleeping);
+        let time = if time_raw >= (1 << 31) {0} else {time_raw};
         if time != 0 {
             self.event_hub.lock().push(time, Event::Wakeup(pid));
         }
@@ -183,7 +188,7 @@ impl ProcessManager {
 
     pub fn exit(&self, pid: Pid, code: ExitCode) {
         self.set_status(pid, Status::Exited(code));
-        }
+    }
      /// Called when a process exit
     fn exit_handler(&self, pid: Pid, proc: &mut Process) {
         for waiter in self.wait_queue[pid].lock().drain(..) {
diff --git a/crate/riscv b/crate/riscv
index a37a65f..f358204 160000
--- a/crate/riscv
+++ b/crate/riscv
@@ -1 +1 @@
-Subproject commit a37a65fa13a00c5aa0068c3f2b5d55af6a37dd93
+Subproject commit f358204af01f2374ab6ed6ea059f724cd5f2fe6f
diff --git a/kernel/src/fs.rs b/kernel/src/fs.rs
index 8e1b7aa..938dff2 100644
--- a/kernel/src/fs.rs
+++ b/kernel/src/fs.rs
@@ -45,8 +45,12 @@ pub fn shell() {
     // start interaction
     loop {
         print!(">> ");
+
         use console::get_line;
         let name = get_line();
+        //use alloc::prelude::ToString;
+        //let name = "waitkill".to_string();
+
         if name == "" {
             continue;
         }
diff --git a/kernel/src/syscall.rs b/kernel/src/syscall.rs
index 2601216..bcc9bf7 100644
--- a/kernel/src/syscall.rs
+++ b/kernel/src/syscall.rs
@@ -113,7 +113,7 @@ fn sys_yield() -> i32 {
 
 /// Kill the process
 fn sys_kill(pid: usize) -> i32 {
-    info!("kill: {}", pid);
+    info!("{} killed: {}", thread::current().id(), pid);
     processor().manager().exit(pid, 0x100);
     if pid == thread::current().id() {
         processor().yield_now();