linux-kernel - Re: [PATCH] cpufreq: CPPC: Increase delay between perf counter reads

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Message-ID: <CAFivqmKZcipdc1P1b7jkNTBAV-WE4bSeW8z=eHHmtHBxuErZiQ@mail.gmail.com>
Date: Tue, 5 Aug 2025 18:00:09 -0700
From: Prashant Malani <pmalani@...gle.com>
To: Yang Shi <yang@...amperecomputing.com>
Cc: open list <linux-kernel@...r.kernel.org>, 
	"open list:CPU FREQUENCY SCALING FRAMEWORK" <linux-pm@...r.kernel.org>, "Rafael J. Wysocki" <rafael@...nel.org>, 
	Viresh Kumar <viresh.kumar@...aro.org>, beata.michalska@....com, 
	Catalin Marinas <catalin.marinas@....com>, Ionela Voinescu <Ionela.Voinescu@....com>
Subject: Re: [PATCH] cpufreq: CPPC: Increase delay between perf counter reads

Thanks Yang,

On Tue, 5 Aug 2025 at 17:26, Yang Shi <yang@...amperecomputing.com> wrote:
> Thank you for cc'ing me the patch. I posted the similar patch ago and
> had some discussion on the mailing list. Then someone else from ARM
> pursued a different way to solve it. But I didn't follow very closely.
> If I remember correctly, a new sysfs interface, called cpuinfo_avg_freq
> was added. It should be the preferred way to get cpu frequency. Please
> see
> https://github.com/torvalds/linux/commit/fbb4a4759b541d09ebb8e391d5fa7f9a5a0cad61.
>
> Added Beata Michalska in the loop too, who is the author of the patch.
> Please feel free to correct me, if I'm wrong.

Thanks for the additional context. Yeah, the issue is that :
- The new sysfs node is sampling period is too long (20ms) [1]
That makes it problematic for userspace use cases, so we need something
which takes less time.
- The central accuracy issue behind cpuinfo_cur_freq still needs to be handled.

[1] https://elixir.bootlin.com/linux/v6.16/source/arch/arm64/kernel/topology.c#L283


-- 
-Prashant