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

[Joel Fernandes]

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.

- Joel