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From: "Rafael J. Wysocki" <rjw@sisk.pl>
To: Denys Fedoryschenko <denys@visp.net.lb>
Subject: Re: 2.6.28 - 2.6.29-rc6-git5 regression, p4-clockmod/cpufreq probably
Date: Mon, 2 Mar 2009 21:34:18 +0100
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Cc: Sitsofe Wheeler <sitsofe@yahoo.com>, Matthew Garrett <mjg@redhat.com>,
       linux-kernel@vger.kernel.org, cpufreq@vger.kernel.org, davej@redhat.com,
       ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
       Len Brown <lenb@kernel.org>
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On Monday 02 March 2009, Denys Fedoryschenko wrote:
> On Monday 02 March 2009 19:23:09 Sitsofe Wheeler wrote:
> > On Mon, Mar 02, 2009 at 06:33:46PM +0200, Denys Fedoryschenko wrote:
> > > CPUFreq infrastructure much more powerful.
> > > -d --min <FREQ>
> > >     new minimum CPU frequency the governor may select.
> > > -u --max <FREQ>
> > >     new maximum CPU frequency the governor may select.
> > > -g --governor <GOV>
> > >     new cpufreq governor.
> > >
> > > This things you cannot do over inserting values over ACPI. Sure you can
> > > reinvent the wheel, but why?
> >
> > I guess I don't understand why you would want scaling if it didn't save
> > you any power...
> If i will limit current in certain limits, rather than using high current, i 
> will have in result higher efficiency of discharging battery.
> The discharge curves for a Lithium Ion cell below show that the effective 
> capacity of the cell is reduced if the cell is discharged at very high rates 
> (or conversely increased with low discharge rates). This is called the 
> capacity offset and the effect is common to most cell chemistries.
> If the discharge takes place over a long period of several hours as with some 
> high rate applications such as electric vehicles, the effective capacity of 
> the battery can be as much as double the specified capacity at the C rate. 
> This can be most important when dimensioning an expensive battery for high 
> power use. The capacity of low power, consumer electronics batteries is 
> normally specified for discharge at the C rate whereas the SAE uses the 
> discharge over a period of 20 hours (0.05C) as the standard condition for 
> measuring the Amphour capacity of automotive batteries. The graph below shows 
> that the effective capacity of a deep discharge lead acid battery is almost 
> doubled as the discharge rate is reduced from 1.0C to 0.05C. For discharge 
> times less than one hour (High C rates) the effective capacity falls off 
> dramatically. 
> This means even i need to recode on battery movie (clearly need same amount of 
> processing power), if i do it with 100% CPU available let's say in 30 
> minutes, and if i do it with 50% CPU available in 60 minutes, at the end i 
> should have DIFFERENT amount of remaining battery.
> 
> Another example, if i run screensaver i want governor powersave(so some crazy 
> flash plugin don't dry out battery till i come back) , if i run on battery i 
> will put conservative and limit frequency range to max 50% of CPU power, so i 
> can be sure my laptop lasts enough time. This in case battery time matter for 
> me more than computing power. Sure i will prefer some universal way, so i can 
> set same rules on Core 2 Duo based laptop, and cheap Celeron. Cpufreq provide 
> me useful framework for this job, and important SAME API everywhere. Less 
> efficient on p4-clockmod, and very efficient on true "mobile" processors.
> 
> * Many things quoted from http://www.mpoweruk.com/performance.htm

You should have added linux-acpi to the CC list and since the change in
question was very much on purpose, I'm not going to list (at least for now).

Thanks,
Rafael
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