Hi Steven, agreed with your comments in the previous message. Indeed, I missed some points. > On wakeup, we can wake up several RT tasks (as my test case does) and if > we only push one task, then the other tasks may not migrate over to the > other run queues. I logged this happening in my tests. I guess, what may happen is that while we are running push_rt_tasks() on CPU-k (say, as a result on try_to_wake_up(task_1)) and as this_rq->lock may get released (in double_lock_balance()) , we may get in a 'race' with try_to_wake_up(task_2) from (another) CPU-m. It places a woken up task on the same run-queue (for which push_rt_task() is already running on CPU-k) and, actually, run push_rt_task() for the same rq again! So it may happen that both task_1 and task_2 will be pushed from the same CPU... Do you see an error in my description? (it's a late hour so I can miss something again ... sure, otherwise I'm almost perfect :-/ ) Can it correlate with what you have observed in your tests? Otherwise, there is 1:1 relation : push_rt_task() is called for every new (single) task activated by try_to_wake_up() and for a preempted task... so it's not like a few tasks are placed on the run-queue and then push_rt_tasks() is called once. btw., if this scenario may take place... maybe it would make sense to have something like RTLB_INPROGRESS/PENDING and to avoid competing push_rt_tasks() calls for the same 'rq' from different CPUs? (although, there can be some disadvantages here as well. e.g. we would likely need to remove 'max 3 tasks at once' limit and get, theoretically, unbounded time spent in push_rt_tasks() on a single CPU). > > -- Steve > -- Best regards, Dmitry Adamushko - To unsubscribe from this list: send the line "unsubscribe linux-rt-users" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
