Re: [PATCH] cpufreq: Avoid unnecessary frequency updates due to mismatch

From: Viresh Kumar <viresh.kumar@linaro.org>
To: Vincent Guittot <vincent.guittot@linaro.org>
Cc: Rafael Wysocki <rjw@rjwysocki.net>,
	"Rafael J. Wysocki" <rafael@kernel.org>,
	Matthias Brugger <matthias.bgg@gmail.com>,
	linux-pm@vger.kernel.org, Rex-BC Chen <rex-bc.chen@mediatek.com>,
	linux-kernel@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-mediatek@lists.infradead.org
Subject: Re: [PATCH] cpufreq: Avoid unnecessary frequency updates due to mismatch
Date: Thu, 5 May 2022 13:14:08 +0530	[thread overview]
Message-ID: <20220505074408.ayzmd5kdbw2fagbq@vireshk-i7> (raw)
In-Reply-To: <CAKfTPtDbsd+RLwY+0ZfnNWkQD+jOHmoX2K+ZfsOMnEH81ouVjw@mail.gmail.com>

On 05-05-22, 09:28, Vincent Guittot wrote:
> On Wed, 4 May 2022 at 10:21, Viresh Kumar <viresh.kumar@linaro.org> wrote:
> >
> > For some platforms, the frequency returned by hardware may be slightly
> > different from what is provided in the frequency table. For example,
> 
> Do you have more details ?

This is where the problem was discussed.

https://lore.kernel.org/lkml/20220422075239.16437-8-rex-bc.chen@mediatek.com/

> Do you mean that between 2 consecutives reads you can get either
> 500Mhz or 499Mhz ?

No, the hardware always returns something like 499,999,726 Hz, but the
OPP table contains the value 500 MHz. The field policy->cur is set
based on opp table eventually (target_index) and so contains 500MHz,
almost always. But when cpufreq_get() is called, it finds the current
freq is 499 MHz, instead of 500 MHz. And so the issue.

> Or is it a fixed mismatch between the table and the freq returned by HW ?

Yes.

-- 
viresh