Messages in this thread Patch in this message | | | Date | Mon, 01 Mar 2010 23:22:47 +0900 | From | Tejun Heo <> | Subject | Re: [PATCH 07/43] sched: implement try_to_wake_up_local() |
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Hello, Oleg.
On 02/28/2010 09:33 PM, Oleg Nesterov wrote: > Wow ;)
:-)
> I didn't read the whole series yet, still I'd like to ask a couple > of questions right now. Tejun, I am just trying to understand this > code.
Sure.
>> @@ -2438,6 +2438,10 @@ static inline void ttwu_post_activation(struct task_struct *p, struct rq *rq, >> rq->idle_stamp = 0; >> } >> #endif >> + /* >> + * Wake up is complete, fire wake up notifier. This allows >> + * try_to_wake_up_local() to be called from wake up notifiers. >> + */ >> if (success) >> fire_sched_notifiers(p, wakeup); > > Could you explain the comment? ttwu_post_activation() sets state = > TASK_RUNNING few lines above, what try_to_wake_up_local() can do if > called from ->wakeup() notifier ?
It can wake up another task on the same rq.
>> +bool try_to_wake_up_local(struct task_struct *p, unsigned int state, >> + int wake_flags) >> +{ >> ... >> + if (!p->se.on_rq) { >> + if (likely(!task_running(rq, p))) { >> + schedstat_inc(rq, ttwu_count); >> + schedstat_inc(rq, ttwu_local); >> + } >> + ttwu_activate(p, rq, wake_flags & WF_SYNC, false, true); >> + success = true; >> + } > > Shouldn't try_to_wake_up_local() check task_contributes_to_load() to > account ->nr_uninterruptible?
try_to_wake_up() does that because the task may be moved to a different CPU via select_task_rq() for local wakeups, the accounting can be safely handled by activate_task().
>> @@ -5498,6 +5549,11 @@ need_resched_nonpreemptible: >> if (unlikely(signal_pending_state(prev->state, prev))) { >> prev->state = TASK_RUNNING; >> } else { >> + /* >> + * Fire sleep notifier before changing any scheduler >> + * state. This allows try_to_wake_up_local() to be >> + * called from sleep notifiers. >> + */ >> fire_sched_notifiers(prev, sleep); >> deactivate_task(rq, prev, 1); > > Again, I don't understand the comment... If ->sleep() notifier wakes up > this task, we shouldn't do deactivate_task() ? > > Probably both comment mean a notifier could wake up another task bound > to this rq, in this case it looks a bit confusing, imho.
Correct. I'll update the comment.
> Off-topic, but it is a bit sad wait_task_inactive() can not use ->sleep() > notifier to avoid schedule_timeout(), afaics we can't add the notifier > to !current task.
Agreed. The whole thing avoids sync cost by only allowing current to adjust the notifiers and it's a bit sad that wait_task_inactive() can't use it for that.
Thanks.
-- tejun
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