* Ingo Molnar <[email protected]> wrote:
>
> * Nick Piggin <[email protected]> wrote:
>
> > > we could do it in the other direction just as much - i only touched
> > > 3 architectures. Up to Andrew i guess.
> >
> > How about just setting need_resched at the start of the cpu_idle
> > function instead? Rather than changing the structure of the idle loops
> > themselves. That would suit me best.
>
> that's fine with me too.
updated patch below.
--
this patch (ontop of the current -mm scheduler patchset) tweaks
cpu_idle() semantics a bit: it changes the idle loops (that do
preemption) to call the first schedule() unconditionally.
the advantage is that as a result we dont have to set the idle thread's
NEED_RESCHED flag in init_idle(), which in turn makes cond_resched()
even more of an invariant: it can be called even from init code without
it having any effect. A cond resched in the init codepath hangs
otherwise.
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) (note that for now this
patch only covers architectures that use kernel/Kconfig.preempt, but all
other architectures will work just fine too.)
Signed-off-by: Ingo Molnar <[email protected]>
arch/i386/kernel/process.c | 2 ++
arch/ppc64/kernel/idle.c | 1 +
arch/x86_64/kernel/process.c | 2 ++
kernel/sched.c | 10 +++++++++-
4 files changed, 14 insertions(+), 1 deletion(-)
--- linux/kernel/sched.c.orig
+++ linux/kernel/sched.c
@@ -4163,6 +4163,15 @@ 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. Architecture-level cpu_idle()
+ * functions should set it explicitly, before entering their idle-loop.
+ */
void __devinit init_idle(task_t *idle, int cpu)
{
runqueue_t *rq = cpu_rq(cpu);
@@ -4180,7 +4189,6 @@ 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! */
--- linux/arch/x86_64/kernel/process.c.orig
+++ linux/arch/x86_64/kernel/process.c
@@ -162,6 +162,8 @@ EXPORT_SYMBOL_GPL(cpu_idle_wait);
*/
void cpu_idle (void)
{
+ set_tsk_need_resched(current);
+
/* endless idle loop with no priority at all */
while (1) {
while (!need_resched()) {
--- linux/arch/ppc64/kernel/idle.c.orig
+++ linux/arch/ppc64/kernel/idle.c
@@ -305,6 +305,7 @@ static int native_idle(void)
void cpu_idle(void)
{
+ set_tsk_need_resched(current);
idle_loop();
}
--- linux/arch/i386/kernel/process.c.orig
+++ linux/arch/i386/kernel/process.c
@@ -179,6 +179,8 @@ void cpu_idle(void)
{
int cpu = _smp_processor_id();
+ set_tsk_need_resched(current);
+
/* endless idle loop with no priority at all */
while (1) {
while (!need_resched()) {
-
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