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

[Vincent Guittot]

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
is instability between your runs; As an example, run2 without patch
does better than run1 with patchs for 2g and 4g.
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

Vincent
>
> - Joel