Re: Status of X86_P4_CLOCKMOD?

[Dave Jones <davej@redhat.com>]

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