linux-kernel - [PATCH v3 0/3] Add support for AArch64 AMUv1-based arch_freq_get_on

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Message-Id: <20240312083431.3239989-1-beata.michalska@arm.com>
Date: Tue, 12 Mar 2024 08:34:28 +0000
From: Beata Michalska <beata.michalska@....com>
To: linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	ionela.voinescu@....com,
	vanshikonda@...amperecomputing.com
Cc: sudeep.holla@....com,
	will@...nel.org,
	catalin.marinas@....com,
	vincent.guittot@...aro.org,
	sumitg@...dia.com,
	yang@...amperecomputing.com,
	lihuisong@...wei.com
Subject: [PATCH v3 0/3] Add support for AArch64 AMUv1-based arch_freq_get_on_cpu

Introducing arm64 specific version of arch_freq_get_on_cpu, cashing on
existing implementation for FIE and AMUv1 support: the frequency scale
factor, updated on each sched tick, serves as a base for retrieving
the frequency for a given CPU, representing an average frequency
reported between the ticks - thus its accuracy is limited.

The changes have been rather lightly (due to some limitations) tested on
an FVP model.

Relevant discussions:
[1] https://lore.kernel.org/all/20240229162520.970986-1-vanshikonda@os.amperecomputing.com/
[2] https://lore.kernel.org/all/7eozim2xnepacnnkzxlbx34hib4otycnbn4dqymfziqou5lw5u@5xzpv3t7sxo3/
[3] https://lore.kernel.org/all/20231212072617.14756-1-lihuisong@huawei.com/
[4] https://lore.kernel.org/lkml/ZIHpd6unkOtYVEqP@e120325.cambridge.arm.com/T/#m4e74cb5a0aaa353c60fedc6cfb95ab7a6e381e3c

v3:
- dropping changes to cpufreq_verify_current_freq
- pulling in changes from Ionela initializing capacity_freq_ref to 0
  (thanks for that!)  and applying suggestions made by her during last review:
	- switching to arch_scale_freq_capacity and arch_scale_freq_ref when
	  reversing freq scale factor computation
	- swapping shift with multiplication
- adding time limit for considering last scale update as valid
- updating frequency scale factor upon entering idle

v2:
- Splitting the patches
- Adding comment for full dyntick mode
- Plugging arch_freq_get_on_cpu into cpufreq_verify_current_freq instead
  of in show_cpuinfo_cur_freq to allow the framework to stay more in sync
  with potential freq changes

Beata Michalska (2):
  arm64: Provide an AMU-based version of arch_freq_get_on_cpu
  arm64: Update AMU-based frequency scale factor on entering idle

Ionela Voinescu (1):
  arch_topology: init capacity_freq_ref to 0

 arch/arm64/kernel/topology.c | 116 +++++++++++++++++++++++++++++++----
 drivers/base/arch_topology.c |   8 ++-
 2 files changed, 110 insertions(+), 14 deletions(-)

-- 
2.25.1