linux-kernel - Re: [PATCH] cpufreq: Add scaling frequency range support

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Date:	Wed, 29 Jul 2015 02:18:28 +0200
From:	"Rafael J. Wysocki" <rjw@...ysocki.net>
To:	Pan Xinhui <xinhuix.pan@...el.com>
Cc:	Viresh Kumar <viresh.kumar@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pm@...r.kernel.org" <linux-pm@...r.kernel.org>,
	"mnipxh@....com" <mnipxh@....com>,
	"yanmin_zhang@...ux.intel.com" <yanmin_zhang@...ux.intel.com>
Subject: Re: [PATCH] cpufreq: Add scaling frequency range support

On Tuesday, July 28, 2015 12:53:33 PM Pan Xinhui wrote:
> hi, Viresh
> 	thanks for your reply :)
> On 2015年07月28日 12:29, Viresh Kumar wrote:
> > On 28-07-15, 11:32, Pan Xinhui wrote:
> >> From: Pan Xinhui <xinhuix.pan@...el.com>
> >>
> >> Userspace at most time do cpufreq tests very much inconveniently.
> >> Currently they have to echo min and max cpu freq separately like below:
> >> echo 480000  > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
> >> echo 2240000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> >>
> >> Add scaling_freq_range cpufreq attr to support userspace's demand.
> >> Therefore it's easier for testers to write readable scripts like below: 
> >> echo 480000-2240000 >
> >> /sys/devices/system/cpu/cpu0/cpufreq/scaling_freq_range
> > 
> > I don't think this brings any good change, we already have support for
> > that with min/max freqs and I don't see how scripts can be less
> > readable with that.
> > 
> yes, min/max are supported, however it is inconvenient. sometime it's very easy to cause obscure bugs.
> For example, some one might write a script like below.
> echo 480000  > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
> echo 960000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> .....//other works
> echo 1120000  > /sys/devices/system/cpu/cpu0/cpufreq/scaling_min_freq
> echo 2240000 > /sys/devices/system/cpu/cpu0/cpufreq/scaling_max_freq
> ...//other works
> 
> But it did not work when we echo 112000 to min-freq, as the current max freq is smaller than it.
> It's hard to figure it out in a big script... we have many such scripts.

Fix them, then, pretty please.

And adding this attribute is not going to magically fix them, is it?

Thanks,
Rafael

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