Re: [PATCH] sched/fair: Consider RT/IRQ pressure in capacity_spare_wake

[Joel Fernandes]

Hi Vincent,

>>
>>>
>>>> ------------------------------------------------------------
>>>> Here we have RT activity running on big CPU cluster induced with rt-app,
>>>> and running hackbench in parallel. The RT tasks are bound to 4 CPUs on
>>>> the big cluster (cpu 4,5,6,7) and have 100ms periodicity with
>>>> runtime=20ms sleep=80ms.
>>>>
>>>> Hackbench shows big benefit (30%) improvement when number of tasks is 8
>>>> and 32: Note: data is completion time in seconds (lower is better).
>>>> Number of loops for 8 and 16 tasks is 50000, and for 32 tasks its 20000.
>>>> +--------+-----+-------+-------------------+---------------------------+
>>>> | groups | fds | tasks | Without Patch     | With Patch                |
>>>> +--------+-----+-------+---------+---------+-----------------+---------+
>>>> |        |     |       | Mean    | Stdev   | Mean            | Stdev   |
>>>> |        |     |       +-------------------+-----------------+---------+
>>>> |      1 |   8 |     8 | 1.0534  | 0.13722 | 0.7293 (+30.7%) | 0.02653 |
>>>> |      2 |   8 |    16 | 1.6219  | 0.16631 | 1.6391 (-1%)    | 0.24001 |
>>>> |      4 |   8 |    32 | 1.2538  | 0.13086 | 1.1080 (+11.6%) | 0.16201 |
>>>> +--------+-----+-------+---------+---------+-----------------+---------+
>>>
>>>  Out of curiosity, do you know why you don't see any improvement for
>>> 16 tasks but only for 8 and 32 tasks ?
>>
>> Yes I'm not fully sure why 16 tasks didn't show that much improvement.
>
> Yes. This is just to make sure that there no unexpected side effect

Just got back from vacation. Tried to reproduce these results, looks
like our product kernel changed enough that I am not able to exactly
replicate these results and I don't recall the tree I ran these on. I
will redo these tests and share my data in the next rev. Worst case I
can probably drop this test, since there are other hackbench tests in
this patch as well that show improvements. But I'll give it a shot to
make sure no side effects from this. thanks.

- Joel