linux-kernel - Re: [PATCH V2] cpufreq: Make sure CPU is running on a freq from freq-table

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Message-ID: <2065797.S0ijuuXCoe@vostro.rjw.lan>
Date:	Thu, 28 Nov 2013 15:12:57 +0100
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Dirk Brandewie <dirk.brandewie@...il.com>,
	Lists linaro-kernel <linaro-kernel@...ts.linaro.org>,
	Patch Tracking <patches@...aro.org>,
	"cpufreq@...r.kernel.org" <cpufreq@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Nishanth Menon <nm@...com>, Carlos Hernandez <ceh@...com>
Subject: Re: [PATCH V2] cpufreq: Make sure CPU is running on a freq from freq-table

On Thursday, November 28, 2013 07:11:17 PM Viresh Kumar wrote:
> On 28 November 2013 18:39, Rafael J. Wysocki <rjw@...ysocki.net> wrote:
> > acpi-cpufreq is one at least.
> >
> > Anyway, this isn't about ACPI or anything like that, but hardware.  Generally
> > speaking, on modern Intel hardware the processor itself chooses the frequency
> > to run at and it may do that behind your back.  Moreover, it can choose a
> > frequency different from the one you asked for.  And it won't choose one that
> > it can't run at for that matter. :-)
> >
> > Overall, I don't believe that the problem you're trying to address is relevant
> > for any non-exotic x86 hardware.
> 
> Okay.. So wouldn't it be better that we add this special flag only when we
> face a real problem? Otherwise this flag might stay unused for long time
> and then we might end up removing it..
> 
> >> > So there should be a flag for
> >> > drivers indicating whether or not frequencies (or operation points in
> >> > general) are directly testable and the check should only be done for
> >> > the drivers with the flag set.
> >>
> >> Probably a flag with properties exactly opposite to what you mentioned,
> >> so that we don't need to modify most of the drivers..
> >
> > That would work too if you prefer it.
> 
> In case we need this flag, what should we name it?
> ALLOW_UNKNOWN_FREQ ??

SKIP_INITIAL_FREQUENCY_CHECK ?

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