linux-kernel - Re: [PATCH v3 0/5] Rework system pressure interface to the scheduler

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Message-ID: <d37e3d06-d9fc-4fc3-ad92-e7031489660a@arm.com>
Date: Tue, 9 Jan 2024 12:33:59 +0100
From: Dietmar Eggemann <dietmar.eggemann@....com>
To: Vincent Guittot <vincent.guittot@...aro.org>, linux@...linux.org.uk,
 catalin.marinas@....com, will@...nel.org, sudeep.holla@....com,
 rafael@...nel.org, viresh.kumar@...aro.org, agross@...nel.org,
 andersson@...nel.org, konrad.dybcio@...aro.org, mingo@...hat.com,
 peterz@...radead.org, juri.lelli@...hat.com, rostedt@...dmis.org,
 bsegall@...gle.com, mgorman@...e.de, bristot@...hat.com,
 vschneid@...hat.com, lukasz.luba@....com, rui.zhang@...el.com,
 mhiramat@...nel.org, daniel.lezcano@...aro.org, amit.kachhap@...il.com,
 corbet@....net, gregkh@...uxfoundation.org,
 linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
 linux-pm@...r.kernel.org, linux-arm-msm@...r.kernel.org,
 linux-trace-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Cc: qyousef@...alina.io
Subject: Re: [PATCH v3 0/5] Rework system pressure interface to the scheduler

On 08/01/2024 14:48, Vincent Guittot wrote:
> Following the consolidation and cleanup of CPU capacity in [1], this serie
> reworks how the scheduler gets the pressures on CPUs. We need to take into
> account all pressures applied by cpufreq on the compute capacity of a CPU
> for dozens of ms or more and not only cpufreq cooling device or HW
> mitigiations. we split the pressure applied on CPU's capacity in 2 parts:
> - one from cpufreq and freq_qos
> - one from HW high freq mitigiation.
> 
> The next step will be to add a dedicated interface for long standing
> capping of the CPU capacity (i.e. for seconds or more) like the
> scaling_max_freq of cpufreq sysfs. The latter is already taken into
> account by this serie but as a temporary pressure which is not always the
> best choice when we know that it will happen for seconds or more.

I guess this is related to the 'user space system pressure' (*) slide of
your OSPM '23 talk.

Where do you draw the line when it comes to time between (*) and the
'medium pace system pressure' (e.g. thermal and FREQ_QOS).

IIRC, with (*) you want to rebuild the sched domains etc.

> 
> [1] https://lore.kernel.org/lkml/20231211104855.558096-1-vincent.guittot@linaro.org/
> 
> Change since v1:
> - Rework cpufreq_update_pressure()
> 
> Change since v1:
> - Use struct cpufreq_policy as parameter of cpufreq_update_pressure()
> - Fix typos and comments
> - Make sched_thermal_decay_shift boot param as deprecated
> 
> Vincent Guittot (5):
>   cpufreq: Add a cpufreq pressure feedback for the scheduler
>   sched: Take cpufreq feedback into account
>   thermal/cpufreq: Remove arch_update_thermal_pressure()
>   sched: Rename arch_update_thermal_pressure into
>     arch_update_hw_pressure
>   sched/pelt: Remove shift of thermal clock
> 
>  .../admin-guide/kernel-parameters.txt         |  1 +
>  arch/arm/include/asm/topology.h               |  6 +-
>  arch/arm64/include/asm/topology.h             |  6 +-
>  drivers/base/arch_topology.c                  | 26 ++++----
>  drivers/cpufreq/cpufreq.c                     | 36 +++++++++++
>  drivers/cpufreq/qcom-cpufreq-hw.c             |  4 +-
>  drivers/thermal/cpufreq_cooling.c             |  3 -
>  include/linux/arch_topology.h                 |  8 +--
>  include/linux/cpufreq.h                       | 10 +++
>  include/linux/sched/topology.h                |  8 +--
>  .../{thermal_pressure.h => hw_pressure.h}     | 14 ++---
>  include/trace/events/sched.h                  |  2 +-
>  init/Kconfig                                  | 12 ++--
>  kernel/sched/core.c                           |  8 +--
>  kernel/sched/fair.c                           | 63 +++++++++----------
>  kernel/sched/pelt.c                           | 18 +++---
>  kernel/sched/pelt.h                           | 16 ++---
>  kernel/sched/sched.h                          | 22 +------
>  18 files changed, 144 insertions(+), 119 deletions(-)
>  rename include/trace/events/{thermal_pressure.h => hw_pressure.h} (55%)