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

[Vincent Guittot]

On 14 December 2017 at 18:08, Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
> Hi Vincent,
> Thanks for your reply.
>
> On Thu, Dec 14, 2017 at 7:46 AM, Vincent Guittot
> <vincent.guittot@xxxxxxxxxx> wrote:
>> Hi Joel,
>>
>> On 13 December 2017 at 21:00, Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
>>> On Mon, Dec 11, 2017 at 4:43 PM, Joel Fernandes <joelaf@xxxxxxxxxx> wrote:
>>>> 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
>>>>
>>>
>>> It could have been sloppy testing - I could have hit thermal
>>> throttling or forgotten to stop Android runtime before running the
>>> test. Looking at my old data, the case for 16 tasks has higher
>>> completion times than 32 tasks which doesn't make sense. Sorry about
>>> that. I was careful this time, I recreated the product tree and
>>> applied patch - ran the same test as in this patch, the data prefixed
>>> with "with" is with patch and "without" is without patch.
>>>
>>> The naming of the Test column is "<test>-<numFDs>-<numGroups>". Data
>>> is completion time of hackbench in seconds.
>>>
>>> RUN 1:
>>>
>>> Test         Mean             Median            Stddev
>>> with-f4-1g  0.67645 (+3.7%)  0.68000 (+3.8%)  0.025755
>>> with-f4-2g  1.0685  (-0.3%)  1.0570 (+1%)       0.044122
>>> with-f4-4g  1.7558  (+0.7%)  1.7685 (+0.08%)    0.096015
>>>
>>> without-f4-1g  0.70255  0.70750  0.025330
>>> without-f4-2g  1.0653  1.0680  0.040300
>>> without-f4-4g  1.7688  1.7670  0.046341
>>>
>>> RUN 2:
>>>
>>> Test         Mean          Median          Stddev
>>> with-f4-1g  0.68100 (+1%)  0.67800 (+2%)   0.025543
>>> with-f4-2g  1.0242 (+1.5%) 1.0260 (+1.5%)  0.042886
>>> with-f4-4g  1.6100 (+3%)   1.6075 (+3.7%)  0.052677
>>>
>>> without-f4-1g  0.68840  0.69150  0.030988
>>> without-f4-2g  1.0400  1.0420  0.034288
>>> without-f4-4g  1.6636  1.6670  0.056963
>>>
>>>
>>> Let me know what you think, thanks.
>>
>> The improvement has decreased compared to previous results and there
>
> Yes but the previous result was invalid as I mentioned, I controlled
> the environment better this time. Previous result showed 4g completed
> quicker than 2g which wasn't very meaningful.

Yes. It was just to highlight that we don't see improvements for this
test anymore with new results

>
>> is instability between your runs; As an example, run2 without patch
>> does better than run1 with patchs for 2g and 4g.
>
> That's true. The improvement percent isn't stable.
>
>> Could you run tests on a SMP linux kernel instead of  big/LITTLE
>> android in order to have a saner test environnement and remove some
>> possible disturbances
>
> Would it be Ok with you if I just dropped this synthetic test from the
> patch since there are other hackbench results (case 3) from Rohit
> which are on SMP?

Yes you can probably remove it as there is no improvement and others
tests  show improvement


>
> Thanks,
>
> - Joel