diff --git a/ch3-coop/user/src/syscall.rs b/ch3-coop/user/src/syscall.rs
index 0c9f3e1..dc87cde 100644
--- a/ch3-coop/user/src/syscall.rs
+++ b/ch3-coop/user/src/syscall.rs
@@ -29,7 +29,7 @@ pub fn sys_exit(exit_code: i32) -> isize {
     syscall(SYSCALL_EXIT, [exit_code as usize, 0, 0])
 }
 
-pub fn sys_yield() {
-    syscall(SYSCALL_YIELD, [0, 0, 0]);
-}
+// pub fn sys_yield() {
+//     syscall(SYSCALL_YIELD, [0, 0, 0]);
+// }