diff --git a/user/src/bin/race_adder.rs b/user/src/bin/race_adder.rs
index dabead16..68bee9f9 100644
--- a/user/src/bin/race_adder.rs
+++ b/user/src/bin/race_adder.rs
@@ -9,21 +9,23 @@ use user_lib::{exit, thread_create, waittid, get_time};
 use alloc::vec::Vec;
 
 static mut A: usize = 0;
-const PER_THREAD: usize = 2000000;
+const PER_THREAD: usize = 10000;
 const THREAD_COUNT: usize = 8;
 
 unsafe fn f() -> ! {
-    let start = get_time();
+    let mut t = 2usize;
     for _ in 0..PER_THREAD {
         let a = &mut A as *mut usize;
         let cur = a.read_volatile();
+        for _ in 0..500 { t = t * t % 10007; }
         a.write_volatile(cur + 1);
     }
-    exit((get_time() - start) as i32)
+    exit(t as i32)
 }
 
 #[no_mangle]
 pub fn main() -> i32 {
+    let start = get_time();
     let mut v = Vec::new();    
     for _ in 0..THREAD_COUNT {
         v.push(thread_create(f as usize) as usize);
@@ -32,9 +34,7 @@ pub fn main() -> i32 {
     for tid in v.iter() {
         time_cost.push(waittid(*tid));
     }
-    for (i, cost) in time_cost.iter().enumerate() {
-        println!("cost of thread#{} is {}ms", i, cost);
-    }
+    println!("time cost is {}ms", get_time() - start);
     assert_eq!(unsafe { A }, PER_THREAD * THREAD_COUNT);
     0
 }
diff --git a/user/src/bin/race_adder_atomic.rs b/user/src/bin/race_adder_atomic.rs
new file mode 100644
index 00000000..bb2d20e1
--- /dev/null
+++ b/user/src/bin/race_adder_atomic.rs
@@ -0,0 +1,46 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+extern crate alloc;
+
+use user_lib::{exit, thread_create, waittid, get_time, yield_};
+use alloc::vec::Vec;
+use core::sync::atomic::{AtomicBool, Ordering};
+
+static mut A: usize = 0;
+static OCCUPIED: AtomicBool = AtomicBool::new(false);
+const PER_THREAD: usize = 100000;
+const THREAD_COUNT: usize = 8;
+
+unsafe fn f() -> ! {
+    let mut t = 2usize;
+    for _ in 0..PER_THREAD {
+        while OCCUPIED.compare_exchange(false, true, Ordering::Relaxed, Ordering::Relaxed).is_err() {
+            yield_();
+        }
+        let a = &mut A as *mut usize;
+        let cur = a.read_volatile();
+        for _ in 0..500 { t = t * t % 10007; }
+        a.write_volatile(cur + 1);
+        OCCUPIED.store(false, Ordering::Relaxed);
+    }
+    exit(t as i32)
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    let start = get_time();
+    let mut v = Vec::new();    
+    for _ in 0..THREAD_COUNT {
+        v.push(thread_create(f as usize) as usize);
+    }
+    let mut time_cost = Vec::new();
+    for tid in v.iter() {
+        time_cost.push(waittid(*tid));
+    }
+    println!("time cost is {}ms", get_time() - start);
+    assert_eq!(unsafe { A }, PER_THREAD * THREAD_COUNT);
+    0
+}
diff --git a/user/src/bin/race_adder_loop.rs b/user/src/bin/race_adder_loop.rs
new file mode 100644
index 00000000..64e431a4
--- /dev/null
+++ b/user/src/bin/race_adder_loop.rs
@@ -0,0 +1,47 @@
+#![no_std]
+#![no_main]
+
+#[macro_use]
+extern crate user_lib;
+extern crate alloc;
+
+use user_lib::{exit, thread_create, waittid, get_time, yield_};
+use alloc::vec::Vec;
+
+static mut A: usize = 0;
+static mut OCCUPIED: bool = false;
+const PER_THREAD: usize = 10000;
+const THREAD_COUNT: usize = 8;
+
+unsafe fn f() -> ! {
+    let mut t = 2usize;
+    for _ in 0..PER_THREAD {
+        while OCCUPIED { yield_(); }
+        OCCUPIED = true;
+        // enter critical section
+        let a = &mut A as *mut usize;
+        let cur = a.read_volatile();
+        for _ in 0..500 { t = t * t % 10007; }
+        a.write_volatile(cur + 1);
+        // exit critical section
+        OCCUPIED = false;
+    }
+
+    exit(t as i32)
+}
+
+#[no_mangle]
+pub fn main() -> i32 {
+    let start = get_time();
+    let mut v = Vec::new();    
+    for _ in 0..THREAD_COUNT {
+        v.push(thread_create(f as usize) as usize);
+    }
+    let mut time_cost = Vec::new();
+    for tid in v.iter() {
+        time_cost.push(waittid(*tid));
+    }
+    println!("time cost is {}ms", get_time() - start);
+    assert_eq!(unsafe { A }, PER_THREAD * THREAD_COUNT);
+    0
+}