Date: Tue, 28 Feb 2006 15:09:16 -0500
From: Dave Jones <davej@redhat.com>
To: Matt Mackall <mpm@selenic.com>
Cc: Adrian Bunk <bunk@stusta.de>, Dmitry Torokhov <dtor_core@ameritech.net>,
       davej@codemonkey.org.uk, Zwane Mwaikambo <zwane@commfireservices.com>,
       Samuel Masham <samuel.masham@gmail.com>,
       Jan Engelhardt <jengelh@linux01.gwdg.de>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@osdl.org>, cpufreq@lists.linux.org.uk, ak@suse.de
Subject: Re: Status of X86_P4_CLOCKMOD?
Message-ID: <20060228200916.GA326@redhat.com>
Mail-Followup-To: Dave Jones <davej@redhat.com>,
	Matt Mackall <mpm@selenic.com>, Adrian Bunk <bunk@stusta.de>,
	Dmitry Torokhov <dtor_core@ameritech.net>, davej@codemonkey.org.uk,
	Zwane Mwaikambo <zwane@commfireservices.com>,
	Samuel Masham <samuel.masham@gmail.com>,
	Jan Engelhardt <jengelh@linux01.gwdg.de>,
	linux-kernel@vger.kernel.org, Andrew Morton <akpm@osdl.org>,
	cpufreq@lists.linux.org.uk, ak@suse.de
References: <20060214152218.GI10701@stusta.de> <20060222024438.GI20204@MAIL.13thfloor.at> <20060222031001.GC4661@stusta.de> <200602212220.05642.dtor_core@ameritech.net> <20060223195937.GA5087@stusta.de> <20060223204110.GE6213@redhat.com> <20060228194628.GP4650@waste.org>
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On Tue, Feb 28, 2006 at 01:46:29PM -0600, Matt Mackall wrote:
 > On Thu, Feb 23, 2006 at 03:41:10PM -0500, Dave Jones wrote:
 > > On Thu, Feb 23, 2006 at 08:59:37PM +0100, Adrian Bunk wrote:
 > > 
 > >  > > > >  config X86_P4_CLOCKMOD
 > >  > > > > 	depends on EMBEDDED
 > >  > > > 
 > >  > > > This one is an x86_64 only issue, and yes, it's wrong.
 > >  > > 
 > >  > > That's for P4, not X86_64... And since P4 clock modulation does not provide
 > >  > > almost any energy savings it was "hidden" under embedded.
 > >  > 
 > >  > But the EMBEDDED dependency is only on x86_64:
 > >  > 
 > >  > arch/i386/kernel/cpu/cpufreq/Kconfig:
 > >  > config X86_P4_CLOCKMOD
 > >  >         tristate "Intel Pentium 4 clock modulation"
 > >  >         select CPU_FREQ_TABLE
 > >  >         help
 > >  > 
 > >  > arch/x86_64/kernel/cpufreq/Kconfig:
 > >  > config X86_P4_CLOCKMOD
 > >  >         tristate "Intel Pentium 4 clock modulation"
 > >  >         depends on EMBEDDED
 > >  >         help
 > >  > 
 > >  > And if the option is mostly useless, what is it good for?
 > > 
 > > It's sometimes useful in cases where the target CPU doesn't have any better
 > > option (Speedstep/Powernow).  The big misconception is that it
 > > somehow saves power & increases battery life. Not so.
 > > All it does is 'not do work so often'.  The upside of this is
 > > that in some situations, we generate less heat this way.
 > 
 > This is perplexing. Less heat equals less power usage according to the
 > laws of thermodynamics.

you end up taking longer to do the same amount of work, so you
end up using the same overall power.

		Dave
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