Re: PELT initial task load and wake_up_new_task()

[Steve Muckle]

Hi Yuyang,

On 12/13/2015 11:13 AM, Yuyang Du wrote:
> Hi Steve,
> 
> 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.

thanks
Steve
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/