linux-kernel - Re: [PATCH 0/2] fix some problems for cpufreq

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Message-ID: <4004530.x5fm24OG42@vostro.rjw.lan>
Date:	Sat, 29 Nov 2014 23:30:03 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Wang Weidong <wangweidong1@...wei.com>
Cc:	viresh.kumar@...aro.org, linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org, guohanjun@...wei.com
Subject: Re: [PATCH 0/2] fix some problems for cpufreq

On Saturday, November 29, 2014 09:40:02 AM Wang Weidong wrote:
> On 2014/11/29 9:26, Rafael J. Wysocki wrote:
> > On Friday, November 28, 2014 10:43:37 AM Wang Weidong wrote:
> >> Hi Rafael and Viresh
> >>
> >> Sorry to trouble you again. As for:
> >> "acpi-cpufreq: get the cur_freq from acpi_processor_performance states"
> >> I do it again, and add the other patch.
> >>
> >> patch #1: acpi-cpufreq: make the freq_table store the same freq value
> >>
> >> I think it can work. The set of available states which come
> >> from acpi won't change. Just like the power would be remove,
> >> the acpi driver will do that:
> >> call
> >>  ->acpi_processor_ppc_has_changed
> >>  ->cpufreq_update_policy
> >>  ->acpi_ppc_notifier_block.notifier_call
> >>    ->acpi_processor_ppc_notifier
> >>    ->cpufreq_verify_within_limits
> >> The progress will change the policy's min_freq and max_freq
> >> while it won't change the set of states(freq_tables).
> > 
> > OK, so the above information needs to go into the changelog of patch [1/2].
> > Also, please clarify the problem description in that changelog, it is very
> > difficult to understand the way it is now.
> > 
> 
> sure, I should do it.
> 
> >> patch #2: cpufreq: show the real avail freqs with the freq_table
> >>
> >> when the min_freq and max_freq change, we should sync the availble
> >> freqs.
> > 
> > Why?  Do any other cpufreq drivers do that?
> > 
> 
> If some cpufreq drivers support several freqs like this:
> 1.05 Ghz 1.30Ghz 1.70GHz 2.10GHz 2.3GHz
>            |                |
>           min              max
> So what the available freqs is 1.30GHz 1.70GHz 2.10GHz
> 
> when we do cpufreq-info or cat scaling_available_frequencies,
> I think the available freqs table show only show these 3 value,
> not all the values.

That changes an existing user space interface, however, and the
only reason I can figure out from what you're saying is your personal
opinion.  This isn't a good enough reason, however.

What if there are utilities and scripts out there relying on the
current behavior?


-- 
I speak only for myself.
Rafael J. Wysocki, Intel Open Source Technology Center.
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