From: Ingo Molnar <mingo@elte.hu>
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>
---
init/main.c | 7 +++++++
kernel/sched.c | 9 ++++++++-
2 files changed, 15 insertions(+), 1 deletion(-)
diff -puN init/main.c~sched-tweak-idle-thread-setup-semantics init/main.c
--- 25/init/main.c~sched-tweak-idle-thread-setup-semantics 2005-05-31 02:45:59.000000000 -0700
+++ 25-akpm/init/main.c 2005-05-31 02:45:59.000000000 -0700
@@ -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 -puN kernel/sched.c~sched-tweak-idle-thread-setup-semantics kernel/sched.c
--- 25/kernel/sched.c~sched-tweak-idle-thread-setup-semantics 2005-05-31 02:45:59.000000000 -0700
+++ 25-akpm/kernel/sched.c 2005-05-31 02:45:59.000000000 -0700
@@ -4240,6 +4240,14 @@ 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);
@@ -4257,7 +4265,6 @@ void __devinit init_idle(task_t *idle, i
#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! */
_