Messages in this thread | | | Date | Thu, 12 Jan 2012 23:08:53 +0600 | Subject | Re: [Question] sched: Should nr_uninterruptible be decremented in ttwu_do_activate()? | From | Rakib Mullick <> |
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On Thu, Jan 12, 2012 at 1:25 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: > On Thu, 2012-01-12 at 12:09 +0600, Rakib Mullick wrote: >> On Wed, Jan 11, 2012 at 11:29 PM, Peter Zijlstra <a.p.zijlstra@chello.nl> wrote: >> > On Wed, 2012-01-11 at 23:22 +0600, Rakib Mullick wrote: >> >> Hello all, >> >> >> >> In ttwu_do_activate(), we're decrementing nr_uninterruptible if >> >> p->sched_contributes_to_load (for SMP=y). But, we're also decrementing >> >> nr_uninterruptible from activate_task at the same path. Why we're >> >> doing it twice for a single task activation path? >> > >> > activate_task() does: >> > >> > if (task_contributes_to_load(p)) >> > rq->nr_uninterruptible--; >> > >> > Now task_contributes_to_load() reads like: >> > >> > #define task_contributes_to_load(task) \ >> > ((task->state & TASK_UNINTERRUPTIBLE) != 0 && \ >> > (task->flags & PF_FREEZING) == 0) >> > >> > which will be false, since we've set TASK_WAKING. >> >> Enough confusing. TASK_WAKING will be set when called from >> try_to_wake_up(). ttwu_do_activate() gets called from other places: >> scheduler_ipi() and sched_ttwu_pending() (at the time of cpu goes >> down). TASK_WAKING will be not set at that time, > > Yes it will be, the only way to get on that list is throught > ttwu_queue_remote() at which point tasks are TASK_WAKING. > >> moreover it is >> possible that, task has p->sched_contributes_to_load is set and latter >> on gets wake up by sched_ttwu_pending/scheduler_ipi() call. > > That's the entire point. But all ways to ttwu_queue_remote() explicitly > set ->sched_contributes_to_load.
That might be the case for scheduler_ipi(), but when sched_ttwu_pending() gets called when a cpu goes down, all tasks from wake_list of that cpu has been moved without TASK_WAKING is set. For a particular task it might be possible that when it ran previously it had p->sched_contributes_to_load is set. Latter, this task's cpu has been put down and calls sched_ttwu_pending(), then for that task p->sched_contributes_to_load is set and TASK_WAKING is not set. Couldn't be happen?
Thanks, Rakib -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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