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Message-ID: <9f2f5c94-cc9f-4a16-9b70-f00598af8cab@arm.com>
Date: Thu, 28 Mar 2024 08:21:28 +0100
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Subject: Re: [RESEND][PATCH v2 3/4] PM: EM: Add em_dev_update_chip_binning()
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From: Dietmar Eggemann <dietmar.eggemann@arm.com>
To: Lukasz Luba <lukasz.luba@arm.com>
Cc: linux-arm-kernel@lists.infradead.org, sboyd@kernel.org, nm@ti.com,
 linux-samsung-soc@vger.kernel.org, daniel.lezcano@linaro.org,
 rafael@kernel.org, viresh.kumar@linaro.org, krzysztof.kozlowski@linaro.org,
 alim.akhtar@samsung.com, m.szyprowski@samsung.com, mhiramat@kernel.org,
 linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org
References: <20240322110850.77086-1-lukasz.luba@arm.com>
 <20240322110850.77086-4-lukasz.luba@arm.com>
 <eb9f48f6-cca8-405b-82a2-352893a79f14@arm.com>
 <30ee98e9-3d9a-4be8-8127-043f68a7dcb1@arm.com>
 <410c5da7-c79c-4607-9aa3-2e78d991d2d7@arm.com>
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On 27/03/2024 13:55, Dietmar Eggemann wrote:
> On 26/03/2024 21:32, Lukasz Luba wrote:
>>
>>
>> On 3/26/24 10:09, Dietmar Eggemann wrote:
>>> On 22/03/2024 12:08, Lukasz Luba wrote:
> 
> [...]
> 
>>>> +    return em_recalc_and_update(dev, pd, em_table);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(em_dev_update_chip_binning);
>>>
>>> In the previous version of 'chip-binning' you were using the new EM
>>> interface em_dev_compute_costs() (1) which is now replaced by
>>> em_recalc_and_update() -> em_compute_costs().
>>>
>>> https://lkml.kernel.org/r/20231220110339.1065505-2-lukasz.luba@arm.com
>>>
>>> Which leaves (1) still unused.
>>>
>>> That was why my concern back then that we shouldn't introduce EM
>>> interfaces without a user:
>>>
>>> https://lkml.kernel.org/r/8fc499cf-fca1-4465-bff7-a93dfd36f3c8@arm.com
>>>
>>> What happens now with em_dev_compute_costs()?
>>>
>>
>> For now it's not used, but modules which will create new EMs
>> with custom power values will use it. When such a module have
>> e.g. 5 EMs for one PD and only switches on one of them, then
>> this em_dev_compute_costs() will be used at setup for those
>> 5 EMs. Later it won't be used.
>> I don't wanted to combine the registration of new EM with
>> the compute cost, because that will create overhead in the
>> switching to new EM code path. Now we have only ~3us, which
>> was the main goal.
>>
>> When our scmi-cpufreq get the support for EM update this
>> compute cost will be used there.
> 
> OK, I see. I checked the reloadable EM test module and
> em_dev_compute_costs() is used there like you described it.

I had a second look and IMHO the layout is like this:

Internal (1) and external (2,3) 'reloadable EM' use cases:
(EM alloc and free not depicted)

1. Late CPUs booting (CPU capacity adjustment)

 e3f1164fc9ee  PM: EM: Support late CPUs booting and capacity adjustment

 schedule_delayed_work(&em_update_work, ...)

  em_update_workfn()
   em_check_capacity_update()
    em_adjust_new_capacity()
     em_recalc_and_update()       <-- (i)
      em_compute_costs()          <-- (ii)
      em_dev_update_perf_domain() <-- external

2. Reload EM from driver

 22ea02848c07  PM: EM: Add em_dev_compute_costs()
 977230d5d503  PM: EM: Introduce em_dev_update_perf_domain() for EM
               updates

 em_dev_compute_costs()           <-- external
  em_compute_costs()              <-- (ii)
 em_dev_update_perf_domain()      <-- external

3. Chip binning

 this patchset  PM: EM: Add em_dev_update_chip_binning()

 em_dev_update_chip_binning()     <-- external
  em_recalc_and_update()          <-- (i)
   em_compute_costs()             <-- (ii)
   em_dev_update_perf_domain()    <-- external