Messages in this thread | | | Subject | Re: PELT initial task load and wake_up_new_task() | From | Steve Muckle <> | Date | Tue, 15 Dec 2015 10:45:53 -0800 |
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On 12/14/2015 06:24 PM, Yuyang Du wrote: >>> On Fri, Dec 11, 2015 at 06:01:45PM -0800, Steve Muckle wrote: >>>> 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. >>> >>> Since the new task's last_update_time is equal to 0, it will not be decayed. >> >> Can you point me to the code for that logic? I don't see anything that >> prevents the decay when a newly woken task is placed on a different CPU >> via the call chain I mentioned above. My testing also shows the load >> being decayed to zero. >> > You may search the last_update_time, and see it would be treated differently > if it is 0. Hope this may be helpful.
Are you referring to the test in enqueue_entity_load_avg()? If so that isn't called until after remove_entity_load_avg() in this scenario, which has no check on last_update_time.
thanks, Steve
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