In init_entity_runnable_average() the last_update_time is initialized to zero. The task is given max load and utilization as a pessimistic initial estimate.
But if in wake_up_new_task() the task is placed on a CPU other than where it was created, __update_load_avg() will be called via set_task_cpu() -> migrate_task_rq_fair() -> remove_entity_load_avg(). Since last_update_time is zero the delta will be huge and the task's load will be entirely decayed away before it is enqueued at the destination CPU. If last_update_time is initialized to cfs_rq_clock_task() the load will not go away, but it will also then be subtracted from the original CPU in remove_entity_load_avg() if the task is placed on a different CPU, which is bad since it was never added there before. Thinking about this more it seemed questionable to treat the assignment of a task to a new CPU in wake_up_new_task() as a migration given that the task has never executed previously. Would it make sense to call __set_task_cpu() there instead of set_task_cpu()? thanks, Steve -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
