On 07/30, Kirill Tkhai wrote: > > В Вт, 29/07/2014 в 18:19 +0200, Oleg Nesterov пишет: > > On 07/29, Kirill Tkhai wrote: > > > > > > How about this? Everything is inside task_rq_lock() now. The patch > > > became much less. > > > > And with this change task_migrating() is not possible under > > task_rq_lock() or __task_rq_lock(). This means that 1/5 can be simplified > > too. > > It seems to me it won't be useless anyway. In every place we underline > that a task is exactly queued or dequeued, so it's not necessary to remember > whether it is migrating or not. This is a cleanup, though it's big.
But, otoh, when you read the code which does "if (task_queued())" it is not clear whether this code knows that task_migrating() is not possible, or we should treat the task_migrating() state specially. But I agree, this is subjective, I leave this to you and Peter. > > __migrate_swap_task() is probably the notable exception... > > > > Off-topic, but it takes 2 ->pi_lock's. This means it can deadlock with > > try_to_wake_up_local() (if a 3rd process does ttwu() and waits for > > ->on_cpu == 0). But I guess __migrate_swap_task() should not play with > > PF_WQ_WORKER threads. > > Hmm.. I'm surprised, PF_WQ_WORKER threads may be unbound. But it seems > we still can't pass them to try_to_wake_up_local. Why? See wq_worker_sleeping/try_to_wake_up_local in __schedule(). But perhaps I misunderstood you, and probably I was not clear. If wq_worker_sleeping() returns !NULL then both task should be local, surely we do not want to migrate them. Oleg. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
