[PATCH] Tweak idle thread setup semantics

This patch tweaks idle thread setup semantics a bit: instead of setting
NEED_RESCHED in init_idle(), we do an explicit schedule() before calling
into cpu_idle().

This patch, while having no negative side-effects, enables wider use of
cond_resched()s.  (which might happen in the stock kernel too, but it's
particulary important for voluntary-preempt)

Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/init/main.c b/init/main.c
index d324801729ba713938481fd4f3a8199fdc2eb6e9..b5e421e39ede7ec40d61da8345e8115a749dc0df 100644 (file)
--- a/init/main.c
+++ b/init/main.c
@@ -383,6 +383,13 @@ static void noinline rest_init(void)
        numa_default_policy();
        unlock_kernel();
        preempt_enable_no_resched();
+
+       /*
+        * The boot idle thread must execute schedule()
+        * at least one to get things moving:
+        */
+       schedule();
+
        cpu_idle();
 } 
 

diff --git a/kernel/sched.c b/kernel/sched.c
index e2b0d3e4dd067ad4e6df0362f265189ac8d17049..5f2182d42241d20b41a12eb9da9671927b5b36d8 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4166,6 +4166,14 @@ void show_state(void)
        read_unlock(&tasklist_lock);
 }
 
+/**
+ * init_idle - set up an idle thread for a given CPU
+ * @idle: task in question
+ * @cpu: cpu the idle task belongs to
+ *
+ * NOTE: this function does not set the idle thread's NEED_RESCHED
+ * flag, to make booting more robust.
+ */
 void __devinit init_idle(task_t *idle, int cpu)
 {
        runqueue_t *rq = cpu_rq(cpu);
@@ -4183,7 +4191,6 @@ void __devinit init_idle(task_t *idle, int cpu)
 #if defined(CONFIG_SMP) && defined(__ARCH_WANT_UNLOCKED_CTXSW)
        idle->oncpu = 1;
 #endif
-       set_tsk_need_resched(idle);
        spin_unlock_irqrestore(&rq->lock, flags);
 
        /* Set the preempt count _outside_ the spinlocks! */