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

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Message-ID: <21a78951-2d4a-1d6e-0cd8-6a4a75ccb142@nvidia.com>
Date: Wed, 20 Mar 2024 22:22:22 +0530
From: Sumit Gupta <sumitg@...dia.com>
To: Beata Michalska <beata.michalska@....com>, Ionela Voinescu
	<ionela.voinescu@....com>
CC: <linux-kernel@...r.kernel.org>, <linux-arm-kernel@...ts.infradead.org>,
	<vanshikonda@...amperecomputing.com>, <sudeep.holla@....com>,
	<will@...nel.org>, <catalin.marinas@....com>, <vincent.guittot@...aro.org>,
	<yang@...amperecomputing.com>, <lihuisong@...wei.com>, linux-tegra
	<linux-tegra@...r.kernel.org>
Subject: Re: [PATCH v3 0/3] Add support for AArch64 AMUv1-based
 arch_freq_get_on_cpu

Hi Beata,

>> On Tuesday 12 Mar 2024 at 08:34:28 (+0000), Beata Michalska wrote:
>>> 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
>>>
>>
>> Should there have been a patch that adds a call to
>> arch_freq_get_on_cpu() from show_cpuinfo_cur_freq() as well?
>>
>> My understanding from this [1] thread and others referenced there is
>> that was something we wanted.
>>
> Right, so I must have missunderstood that, as the way I did read it was that
> it is acceptable to keep things as they are wrt cpufreq sysfs entries.
> 
> ---
> BR
> Beata
>> [1] https://lore.kernel.org/lkml/2cfbc633-1e94-d741-2337-e1b0cf48b81b@nvidia.com/
>>
>> Thanks,
>> Ionela.
>>

Yes, the change to show_cpuinfo_cur_freq from [1] is needed.

[1] 
https://lore.kernel.org/lkml/20230606155754.245998-1-beata.michalska@arm.com/

Thank you,
Sumit Gupta