linux-kernel - Re: [PATCH v6 6/7][Resend] cpufreq: Support for fast frequency switching

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Date:	Tue, 29 Mar 2016 14:10:17 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Viresh Kumar <viresh.kumar@...aro.org>
Cc:	Linux PM list <linux-pm@...r.kernel.org>,
	Juri Lelli <juri.lelli@....com>,
	Steve Muckle <steve.muckle@...aro.org>,
	ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>,
	Vincent Guittot <vincent.guittot@...aro.org>,
	Michael Turquette <mturquette@...libre.com>,
	Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH v6 6/7][Resend] cpufreq: Support for fast frequency switching

On Monday, March 28, 2016 12:33:41 PM Viresh Kumar wrote:
> forgot to review acpi update earlier ..
> 
> On 22-03-16, 02:53, Rafael J. Wysocki wrote:
> > Index: linux-pm/drivers/cpufreq/acpi-cpufreq.c
> > ===================================================================
> > --- linux-pm.orig/drivers/cpufreq/acpi-cpufreq.c
> > +++ linux-pm/drivers/cpufreq/acpi-cpufreq.c
> > @@ -458,6 +458,43 @@ static int acpi_cpufreq_target(struct cp
> >  	return result;
> >  }
> >  
> > +unsigned int acpi_cpufreq_fast_switch(struct cpufreq_policy *policy,
> > +				      unsigned int target_freq)
> > +{
> > +	struct acpi_cpufreq_data *data = policy->driver_data;
> > +	struct acpi_processor_performance *perf;
> > +	struct cpufreq_frequency_table *entry;
> > +	unsigned int next_perf_state, next_freq, freq;
> > +
> > +	/*
> > +	 * Find the closest frequency above target_freq.
> > +	 *
> > +	 * The table is sorted in the reverse order with respect to the
> > +	 * frequency and all of the entries are valid (see the initialization).
> > +	 */
> > +	entry = data->freq_table;
> > +	do {
> > +		entry++;
> > +		freq = entry->frequency;
> > +	} while (freq >= target_freq && freq != CPUFREQ_TABLE_END);
> 
> Consider this table:
> 
> 11000
> 10000
> 9000
> 
> And a target-freq of 10000.
> 
> Wouldn't you end up selecting 11000 ? Or did I misread it ?

In that case the loop will break for freq = 9000 (as per the above
freq >= freq_target check), so it looks like you've misread it.

Thanks,
Rafael