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SubjectRe: [PATCH v4 2/2] sched/fair: update scale invariance of PELT
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On 10/25/18 12:43 PM, Vincent Guittot wrote:
> On Thu, 25 Oct 2018 at 12:36, Dietmar Eggemann <dietmar.eggemann@arm.com> wrote:

[...]

>> I have a couple of questions related to the tests you ran.
>>
>>> On a hikey (octo ARM platform).
>>> Performance cpufreq governor and only shallowest c-state to remove variance
>>> generated by those power features so we only track the impact of pelt algo.
>>
>> So you disabled c-state 'cpu-sleep' and 'cluster-sleep'?
>
> yes
>
>>
>> I get 'hisi_thermal f7030700.tsensor: THERMAL ALARM: 66385 > 65000' on
>> my hikey620. Did you change the thermal configuration? Not sure if there
>> are any actions attached to this warning though.
>
> I have a fan to ensure that no thermal mitigation will bias the measurement.

Great, with a fan they disappear here as well.

>>> each test runs 16 times
>>>
>>> ./perf bench sched pipe
>>> (higher is better)
>>> kernel tip/sched/core + patch
>>> ops/seconds ops/seconds diff
>>> cgroup
>>> root 59648(+/- 0.13%) 59785(+/- 0.24%) +0.23%
>>> level1 55570(+/- 0.21%) 56003(+/- 0.24%) +0.78%
>>> level2 52100(+/- 0.20%) 52788(+/- 0.22%) +1.32%
>>>
>>> hackbench -l 1000
>>
>> Shouldn't this be '-l 100'?
>
> I have re checked and it's -l 1000

Strange, when I run hackbench on this board (performance governor) I get
values like:

root@h620:/# hackbench -l 100
Running in process mode with 10 groups using 40 file descriptors each
(== 400 tasks)
Each sender will pass 100 messages of 100 bytes
Time: 4.023

root@h620:/# hackbench -l 1000
Running in process mode with 10 groups using 40 file descriptors each
(== 400 tasks)
Each sender will pass 1000 messages of 100 bytes
Time: 37.883

Since you have values in the range of 4-6 secs in your hackbench table?
Maybe different hackbench versions?

>>> (lower is better)
>>> kernel tip/sched/core + patch
>>> duration(sec) duration(sec) diff
>>> cgroup
>>> root 4.472(+/- 1.86%) 4.346(+/- 2.74%) -2.80%
>>> level1 5.039(+/- 11.05%) 4.662(+/- 7.57%) -7.47%
>>> level2 5.195(+/- 10.66%) 4.877(+/- 8.90%) -6.12%
>>>
>>> The responsivness of PELT is improved when CPU is not running at max
>>> capacity with this new algorithm. I have put below some examples of
>>> duration to reach some typical load values according to the capacity of the
>>> CPU with current implementation and with this patch.
>>>
>>> Util (%) max capacity half capacity(mainline) half capacity(w/ patch)
>>> 972 (95%) 138ms not reachable 276ms
>>> 486 (47.5%) 30ms 138ms 60ms
>>> 256 (25%) 13ms 32ms 26ms
>>
>> Could you describe these testcases in more detail?
>
> You don't need to run test case. These numbers are computed based on
> geometric series and half period value

Ah, ok, maybe you can mention this explicitly.

[...]

>> What's the initial utilization value of t1? I assume t1 starts with
>> utilization=512 (post_init_entity_util_avg()).

OK, then it's starts at 0.

>>> On my hikey (octo ARM platform) with schedutil governor, the time to reach
>>> max OPP when starting from a null utilization, decreases from 223ms with
>>> current scale invariance down to 121ms with the new algorithm. For this
>>> test, I have enable arch_scale_freq for arm64.
>>
>> Isn't the arch-specific arch_scale_freq_capacity() enabled by default on
>> arm64 with cpufreq support?
>
> Yes. that's a remain of previous version when arch_scale_freq was not yet merged

OK.

[...]

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