Re: [PATCH 22/22] sched: Remove TASK_WAKING

Peter Zijlstra
2011-03-16T09:51:32Z

On Thu, 2011-03-10 at 17:49 -0800, Frank Rowand wrote:
> On 03/02/11 09:38, Peter Zijlstra wrote:
> > With the new locking TASK_WAKING has become obsolete, remove it.
> >
> > Suggested-by: Oleg Nesterov <oleg@redhat.com>
> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@chello.nl>
> > LKML-Reference: <new-submission>
> > ---
>
> < snip >
>
> > Index: linux-2.6/kernel/sched.c
> > ===================================================================
> > --- linux-2.6.orig/kernel/sched.c
> > +++ linux-2.6/kernel/sched.c
> > @@ -2175,7 +2175,7 @@ void set_task_cpu(struct task_struct *p,
> > * We should never call set_task_cpu() on a blocked task,
> > * ttwu() will sort out the placement.
> > */
> > - WARN_ON_ONCE(p->state != TASK_RUNNING && p->state != TASK_WAKING &&
> > + WARN_ON_ONCE(p->state != TASK_RUNNING &&
> > !(task_thread_info(p)->preempt_count & PREEMPT_ACTIVE));
> >
> > #ifdef CONFIG_LOCKDEP
> > @@ -2613,7 +2613,7 @@ try_to_wake_up(struct task_struct *p, un
> > smp_rmb();
> >
> > p->sched_contributes_to_load = !!task_contributes_to_load(p);
> > - p->state = TASK_WAKING;
> > + p->state = TASK_RUNNING;
> >
> > if (p->sched_class->task_waking)
> > p->sched_class->task_waking(p);
>
> No harm if the coded as in the patch, but an alternate suggestion
> if you like it:
>
> The only reason left for "p->state = TASK_RUNNING;" here is when
> cpu is remote. If cpu is not remote then p->state will be set by:
>
> ttwu_queue()
> ttwu_do_activate()
> ttwu_do_wakeup()
> p->state = TASK_RUNNING;
>
> It would be more clear that setting state to TASK_RUNNING is protecting
> the process until it has been removed from the wake_list by
> sched_ttwu_pending() by setting p->state = TASK_RUNNING in ttwu_queue_remote().
>

Yeah, its a bit of a maze.. maybe we should just drop this and keep the
slightly redundant but more clear TASK_WAKING around.