Re: 2.6.2: P4 ClockMod speed

[Dominik Brodowski <linux@dominikbrodowski.de>]

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On Mon, Feb 16, 2004 at 09:48:25PM +0000, dual_bereta_r0x wrote:
> >>locked on cpu *real* speed.
> >
> >
> >It's just a change of appearance -- the cpufreq driver uses the theoretical
> >speed of the CPU for its calculations; the actual CPU speed isn't
> >affected. You can verify this by looking at /proc/cpuinfo which still tells
> >3124.376 MHz.
> >
> >By doing so it becomes easier to enter different frequencies e.g. into
> >/sys/devices/system/cpu/cpufreq/scaling_setspeed -- on my desktop, typing 
> >in
> >1200000 is easier than 12121224... [*]
> 
> Sure but if i want to downgrade it, for example, by night, to a lower 
> speed, and then next day return it to full power? Will I stuck at 2.4GHz?

No, it will run at the same speed as before -- the ratio between actual
cpu_khz and cpufreq/scaling_setspeed will always be the same.

> >[*] The _actual_ CPU speed should be used on all cpufreq drivers where this
> >specific CPU frequency has implications to external components, e.g. LCD,
> >memory or pcmcia devices. Where only the _frequency ratio_ is of importance
> >[for loops_per_jiffy and friends] such "rounding" is acceptable, as long as
> >the ratio is constant.
> 
> Indeed. I'll showing in LCD a lower speed than the running.

That's not the point: some hardware (e.g. ARM) needs different memory
settings and different settings of the LCD controller  for different 
CPU frequencies, as the Front Side Bus of the CPU is closely related 
to the CPU frequency. On x86, all cpufreq techniques I've
seen so far do not modify the FSB [*], so memory settings etc. do not need
to be modified.

	Dominik

[*] or scaling the FSB didn't work...

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