linux-kernel - Re: [PATCH v10 2/4] cpufreq: Introduce an optional cpuinfo_avg

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Message-ID: <20250205070104.6k4n3zcyuki366am@vireshk-i7>
Date: Wed, 5 Feb 2025 12:31:04 +0530
From: Viresh Kumar <viresh.kumar@...aro.org>
To: Beata Michalska <beata.michalska@....com>
Cc: linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-pm@...r.kernel.org, ionela.voinescu@....com,
	sudeep.holla@....com, will@...nel.org, catalin.marinas@....com,
	rafael@...nel.org, sumitg@...dia.com, yang@...amperecomputing.com,
	vanshikonda@...amperecomputing.com, lihuisong@...wei.com,
	zhanjie9@...ilicon.com, ptsm@...ux.microsoft.com,
	Jonathan Corbet <corbet@....net>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>, Borislav Petkov <bp@...en8.de>,
	Dave Hansen <dave.hansen@...ux.intel.com>,
	"H . Peter Anvin" <hpa@...or.com>, Phil Auld <pauld@...hat.com>,
	x86@...nel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH v10 2/4] cpufreq: Introduce an optional cpuinfo_avg_freq
 sysfs entry

On 31-01-25, 16:24, Beata Michalska wrote:
> Currently the CPUFreq core exposes two sysfs attributes that can be used
> to query current frequency of a given CPU(s): namely cpuinfo_cur_freq
> and scaling_cur_freq. Both provide slightly different view on the
> subject and they do come with their own drawbacks.
> 
> cpuinfo_cur_freq provides higher precision though at a cost of being
> rather expensive. Moreover, the information retrieved via this attribute
> is somewhat short lived as frequency can change at any point of time
> making it difficult to reason from.
> 
> scaling_cur_freq, on the other hand, tends to be less accurate but then
> the actual level of precision (and source of information) varies between
> architectures making it a bit ambiguous.
> 
> The new attribute, cpuinfo_avg_freq, is intended to provide more stable,
> distinct interface, exposing an average frequency of a given CPU(s), as
> reported by the hardware, over a time frame spanning no more than a few
> milliseconds. As it requires appropriate hardware support, this
> interface is optional.
> 
> Note that under the hood, the new attribute relies on the information
> provided by arch_freq_get_on_cpu, which, up to this point, has been
> feeding data for scaling_cur_freq attribute, being the source of
> ambiguity when it comes to interpretation. This has been amended by
> restoring the intended behavior for scaling_cur_freq, with a new
> dedicated config option to maintain status quo for those, who may need
> it.
> 
> CC: Jonathan Corbet <corbet@....net>
> CC: Thomas Gleixner <tglx@...utronix.de>
> CC: Ingo Molnar <mingo@...hat.com>
> CC: Borislav Petkov <bp@...en8.de>
> CC: Dave Hansen <dave.hansen@...ux.intel.com>
> CC: H. Peter Anvin <hpa@...or.com>
> CC: Phil Auld <pauld@...hat.com>
> CC: x86@...nel.org
> CC: linux-doc@...r.kernel.org
> 
> Signed-off-by: Beata Michalska <beata.michalska@....com>
> Reviewed-by: Prasanna Kumar T S M <ptsm@...ux.microsoft.com>
> Reviewed-by: Sumit Gupta <sumitg@...dia.com>

Acked-by: Viresh Kumar <viresh.kumar@...aro.org>

-- 
viresh