linux-kernel - Re: [PATCH v5 22/23] PM: EM: Add em_dev_compute

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Message-ID: <4c719764-7f30-4a22-8fcf-ebfd3cdcddb1@arm.com>
Date: Wed, 20 Dec 2023 11:14:29 +0000
From: Lukasz Luba <lukasz.luba@....com>
To: Qais Yousef <qyousef@...alina.io>,
 Dietmar Eggemann <dietmar.eggemann@....com>,
 Xuewen Yan <xuewen.yan94@...il.com>
Cc: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
 rafael@...nel.org, rui.zhang@...el.com, amit.kucheria@...durent.com,
 amit.kachhap@...il.com, daniel.lezcano@...aro.org, viresh.kumar@...aro.org,
 len.brown@...el.com, pavel@....cz, mhiramat@...nel.org, wvw@...gle.com
Subject: Re: [PATCH v5 22/23] PM: EM: Add em_dev_compute_costs() as API for
 device drivers

Hi Dietmar, Qais, Xuewen,

On 12/18/23 11:56, Lukasz Luba wrote:
> Hi Dietmar and Qais,
> 
> On 12/17/23 18:03, Qais Yousef wrote:
>> On 12/12/23 19:50, Dietmar Eggemann wrote:
>>> On 29/11/2023 12:08, Lukasz Luba wrote:
>>>> The device drivers can modify EM at runtime by providing a new EM 
>>>> table.
>>>> The EM is used by the EAS and the em_perf_state::cost stores
>>>> pre-calculated value to avoid overhead. This patch provides the API for
>>>> device drivers to calculate the cost values properly (and not duplicate
>>>> the same code).
>>>
>>> New interface w/o any users? Can we not remove this from this patch-set
>>> and introduce it with the first user(s)?
> 
> I didn't wanted to introduce the user of this in the same patch set.
> I will send a follow up patch for Exynos SoC. More about this below.
> 
>>
>> It's a chicken and egg problem. No interface, will not enable the new 
>> users to
>> appear too. So assuming the interface makes sense, I vote to keep it.
> 
> There are already in mainline platforms which will benefit from this
> feature and would use this API. The platform which support chip
> binning and adjust the voltage based on that information. It can be a
> driver which can even be built as a module. One example is Exynos5 ASV
> (Adaptive Supply Voltage) part of the Exynos chipid driver [1].
> Here is the dmesg log with some additional debug from this driver.
> As you can see the EM finished the registration and also update (the
> new feature from this patch set), but it worked on old Voltages from
> OPPs. (Also, this driver can be built as a module).
> 
> -------------------------------------------------
> [    4.651049] cpu cpu4: EM: created perf domain
> [    4.654073] cpu cpu0: EM: OPP:1200000 is inefficient
> [    4.654108] cpu cpu0: EM: OPP:1100000 is inefficient
> [    4.654140] cpu cpu0: EM: OPP:900000 is inefficient
> [    4.654173] cpu cpu0: EM: OPP:800000 is inefficient
> [    4.654204] cpu cpu0: EM: OPP:600000 is inefficient
> [    4.654235] cpu cpu0: EM: OPP:500000 is inefficient
> [    4.654266] cpu cpu0: EM: OPP:400000 is inefficient
> [    4.654297] cpu cpu0: EM: OPP:200000 is inefficient
> [    4.654342] cpu cpu0: EM: updated
> ....
> [    4.750026] exynos-chipid 10000000.chipid: cpu0 opp0, freq: 1500 missing
> [    4.755329] exynos-chipid 10000000.chipid: Checking asv_volt=1175000 
> opp_volt=1275000
> [    4.763213] exynos-chipid 10000000.chipid: Checking asv_volt=1125000 
> opp_volt=1250000
> [    4.770982] exynos-chipid 10000000.chipid: Checking asv_volt=1075000 
> opp_volt=1250000
> [    4.778820] exynos-chipid 10000000.chipid: Checking asv_volt=1037500 
> opp_volt=1250000
> [    4.786515] exynos-chipid 10000000.chipid: Checking asv_volt=1000000 
> opp_volt=1100000
> [    4.794356] exynos-chipid 10000000.chipid: Checking asv_volt=962500 
> opp_volt=1100000
> [    4.802018] exynos-chipid 10000000.chipid: Checking asv_volt=925000 
> opp_volt=1100000
> [    4.816323] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.824109] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.839933] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.854762] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.866191] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    4.878812] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    4.886052] exynos-chipid 10000000.chipid: cpu4 opp0, freq: 2100 missing
> [    4.892800] exynos-chipid 10000000.chipid: Checking asv_volt=1225000 
> opp_volt=1312500
> [    4.900542] exynos-chipid 10000000.chipid: Checking asv_volt=1162500 
> opp_volt=1262500
> [    4.908342] exynos-chipid 10000000.chipid: Checking asv_volt=1112500 
> opp_volt=1237500
> [    4.916066] exynos-chipid 10000000.chipid: Checking asv_volt=1075000 
> opp_volt=1250000
> [    4.923926] exynos-chipid 10000000.chipid: Checking asv_volt=1037500 
> opp_volt=1250000
> [    4.931707] exynos-chipid 10000000.chipid: Checking asv_volt=1000000 
> opp_volt=1100000
> [    4.939582] exynos-chipid 10000000.chipid: Checking asv_volt=975000 
> opp_volt=1100000
> [    4.947225] exynos-chipid 10000000.chipid: Checking asv_volt=950000 
> opp_volt=1100000
> [    4.954885] exynos-chipid 10000000.chipid: Checking asv_volt=925000 
> opp_volt=1000000
> [    4.962601] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.974047] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.974071] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=1000000
> [    4.993670] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.001163] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.008818] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.016318] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.023955] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.039723] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.054445] exynos-chipid 10000000.chipid: Checking asv_volt=900000 
> opp_volt=900000
> [    5.066709] exynos-chipid 10000000.chipid: Exynos: CPU[EXYNOS5800] 
> PRO_ID[0xe5422000] REV[0x1] Detected
> 
> -------------------------------------------------
> 
> The new EM which would be updated from that driver, would have lower
> voltages as well as different 'inefficient OPPs'. The maximum voltage
> difference based on the tables is 13.54% which means for the dynamic
> power:
> 1362500 = 1.135416667 * 1200000
> P_dyn = C* f * (V*1.1354 * V*1.1354) = C*f*V^2 * 1.289
> 
> That's ~29% different dynamic power (for one core).
> 
> This Voltage adjustment is due to chip lottery. Different SoC vendors
> use different name for this fact.
> I only have this Exynos platform, but when this API
> and v5 features get in, the vendors can modify their drivers and test.
> 
> This should help both: EAS and IPA/DTPM.
> 
> Regards,
> Lukasz
> 
> [1] 
> https://elixir.bootlin.com/linux/latest/source/drivers/soc/samsung/exynos5422-asv.c
> 

Because you wanted to see how this API is going to be used after
boot, I have send a follow-up patch for the OPP framework and Exynos
chip driver [1].

You can see there that all drivers which would need this feature would
share/use the same code in OPP. That OPP uses the EM new APIs.

I don't want to combine this as well in one step in this patch set.
I rather follow step-by-step development like in Arm SCMI.

Regards,
Lukasz

https://lore.kernel.org/lkml/20231220110339.1065505-1-lukasz.luba@arm.com/