From 9f4a804e30df5ab3e8bb9d95d6bd870945f973c2 Mon Sep 17 00:00:00 2001
From: Paul Pan <i@0x7f.app>
Date: Thu, 29 Aug 2024 20:41:34 +0800
Subject: [PATCH] feat: kernel/scheduler: skip idle thread if there are any
 other threads available to run

---
 kernel/src/scheduler.rs | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/kernel/src/scheduler.rs b/kernel/src/scheduler.rs
index 314e131..91349c0 100644
--- a/kernel/src/scheduler.rs
+++ b/kernel/src/scheduler.rs
@@ -2,7 +2,7 @@ use crate::objects::*;
 use core::sync::atomic::AtomicPtr;
 use log::{error, trace};
 use spin::lazy::Lazy;
-use tcb::SCHED_QUEUE_LINK_ID;
+use tcb::{ThreadState, SCHED_QUEUE_LINK_ID};
 use utils::{container_of_mut, linked_list::Link};
 
 #[thread_local]
@@ -38,10 +38,29 @@ impl Scheduler {
         self.head.prepend(tcb);
     }
 
+    pub fn add_next(&self, tcb: &TcbObject) {
+        self.head.append(tcb);
+    }
+
     pub fn schedule(&self) {
+        let mut idle_found = false;
+
         while let Some(next) = self.head.next_mut() {
-            if next.timetick() > 0 && next.schedulable() {
-                trace!("Scheduling thread {}", next.tid());
+            if next.state() == ThreadState::Idle {
+                debug_assert!(next.tid() == 0, "IDLE thread should have TID 0");
+
+                if !idle_found {
+                    // we are meeting the idle thread for the first time, bypass it
+                    idle_found = true;
+                } else {
+                    // no other thread could be scheduled
+                    trace!("[Scheduler] Scheduling IDLE thread");
+                    next.refill_timetick();
+                    next.activate();
+                }
+            } else if next.timetick() > 0 && next.schedulable() {
+                trace!("[Scheduler] Scheduling thread {}", next.tid());
+                idle_found = false;
                 next.activate();
             } else if next.timetick() == 0 {
                 next.refill_timetick();