Re: Status of X86_P4_CLOCKMOD?

From: Matt Mackall <mpm@selenic.com>
To: Dave Jones <davej@redhat.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
Subject: Re: Status of X86_P4_CLOCKMOD?
Date: Tue, 28 Feb 2006 13:46:29 -0600	[thread overview]
Message-ID: <20060228194628.GP4650@waste.org> (raw)
In-Reply-To: <20060223204110.GE6213@redhat.com>

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.

-- 
Mathematics is the supreme nostalgia of our time.