Messages in this thread | | | Date | Mon, 3 Jul 2023 12:08:57 +0100 | Subject | Re: [PATCH v2 00/17] Introduce runtime modifiable Energy Model | From | Lukasz Luba <> |
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Hi Rafael,
On 5/24/23 18:25, Rafael J. Wysocki wrote: > Hi Lukasz, > > On Fri, May 12, 2023 at 11:58 AM Lukasz Luba <lukasz.luba@arm.com> wrote: >> >> Hi all, >> >> This patch set adds a new feature which allows to modify Energy Model (EM) >> power values at runtime. It will allow to better reflect power model of >> a recent SoCs and silicon. Different characteristics of the power usage >> can be leveraged and thus better decisions made during task placement in EAS. >> >> It's part of feature set know as Dynamic Energy Model. It has been presented >> and discussed recently at OSPM2023 [3]. This patch set implements the 1st >> improvement for the EM. >> >> The concepts: >> 1. The CPU power usage can vary due to the workload that it's running or due >> to the temperature of the SoC. The same workload can use more power when the >> temperature of the silicon has increased (e.g. due to hot GPU or ISP). >> In such situation or EM can be adjusted and reflect the fact of increased >> power usage. That power increase is due to a factor called static power >> (sometimes called simply: leakage). The CPUs in recent SoCs are different. >> We have heterogeneous SoCs with 3 (or even 4) different microarchitectures. >> They are also built differently with High Performance (HP) cells or >> Low Power (LP) cells. They are affected by the temperature increase >> differently: HP cells have bigger leakage. The SW model can leverage that >> knowledge. >> 2. It is also possible to change the EM to better reflect the currently >> running workload. Usually the EM is derived from some average power values >> taken from experiments with benchmark (e.g. Dhrystone). The model derived >> from such scenario might not represent properly the workloads usually running >> on the device. Therefore, runtime modification of the EM allows to switch to >> a different model, when there is a need. >> 3. The EM can be adjusted after boot, when all the modules are loaded and >> more information about the SoC is available e.g. chip binning. This would help >> to better reflect the silicon characteristics. Thus, this EM modification >> API allows it now. It wasn't possible in the past and the EM had to be >> 'set in stone'. >> >> Some design details: >> The internal mechanisms for the memory allocation are handled internally in the >> EM. Kernel modules can just call the new API to update the EM data and the >> new memory would be provided and owned by the EM. The EM memory is used by >> EAS, which impacts those design decisions. The EM writers are protected by >> a mutex. This new runtime modified EM table is protected using RCU mechanism, >> which fits the current EAS hot path (which already uses RCU read lock). >> The unregister API handles only non-CPU (e.g. GPU, ISP) devices and uses the >> same mutex as EM modifiers to make sure the memory is safely freed. >> >> More detailed explanation and background can be found in presentations >> during LPC2022 [1][2] or in the documentation patches. >> >> Changelog: >> v2: >> - solved build warning of unused variable in patch 13/17 when EM is >> not compiled in, e.g. on Intel platform for this cpufreq_cooling >> - re-based on top of v6.4-rc1 >> v1: >> - implementation can be found here [4] >> >> [1] https://lpc.events/event/16/contributions/1341/attachments/955/1873/Dynamic_Energy_Model_to_handle_leakage_power.pdf >> [2] https://lpc.events/event/16/contributions/1194/attachments/1114/2139/LPC2022_Energy_model_accuracy.pdf >> [3] https://www.youtube.com/watch?v=2C-5uikSbtM&list=PL0fKordpLTjKsBOUcZqnzlHShri4YBL1H >> [4] https://lore.kernel.org/lkml/20230314103357.26010-1-lukasz.luba@arm.com/ >> >> Lukasz Luba (17): >> PM: EM: Refactor em_cpufreq_update_efficiencies() arguments >> PM: EM: Find first CPU online while updating OPP efficiency >> PM: EM: Refactor em_pd_get_efficient_state() to be more flexible >> PM: EM: Create a new function em_compute_costs() >> trace: energy_model: Add trace event for EM runtime modifications >> PM: EM: Add update_power() callback for runtime modifications >> PM: EM: Check if the get_cost() callback is present in >> em_compute_costs() >> PM: EM: Introduce runtime modifiable table >> PM: EM: Add RCU mechanism which safely cleans the old data >> PM: EM: Add runtime update interface to modify EM power >> PM: EM: Use runtime modified EM for CPUs energy estimation in EAS >> PM: EM: Add argument to get_cost() for runtime modification >> PM: EM: Refactor struct em_perf_domain and add default_table >> Documentation: EM: Add a new section about the design >> Documentation: EM: Add a runtime modifiable EM design description >> Documentation: EM: Add example with driver modifying the EM >> Documentation: EM: Describe the API of runtime modifications > > I haven't seen any responses from anyone having a vested interest in > the Energy Model code. > > I'm not sure what this means, but I surely can't do much about it > myself without any input from the potentially interested parties.
My apologies for the delay. Correct, it has been missing attention, but now Dietmar is reviewing the stuff. He commented a few things and I'm going to respond and address them in v3.
Thanks for having a look into this thread!
Lukasz
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