# Does CPU frequency scaling work with an ordinary P4?

## curmudgeon

I have it working fine on several laptops and "core" processors, but not on (now old) P4s.

All of them work with (only) CONFIG_X86_ACPI_CPUFREQ set to yes.

The help message for this option (2.6.31-r6) states:

"This driver also supports Intel Enhanced Speedstep."

The .config help message for CONFIG_X86_P4_CLOCKMOD says:

"This adds the CPUFreq driver for Intel Pentium 4 / XEON processors.  When enabled it will lower CPU temperature by skipping clocks.

"This driver should be only used in exceptional circumstances when very low power is needed because it causes severe slowdowns and noticeable latencies.  Normally Speedstep should be used instead."

The help messages for the Speedstep drivers (CONFIG_X86_SPEEDSTEP_ICH and CONFIG_X86_SPEEDSTEP_SMI) only talk about mobile processors.

Does that mean P4s are only "ordinary" Speedstep (or do they support frequency scaling at all? Does that mean I should not attempt to use frequency scaling on them?

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## Gusar

 *curmudgeon wrote:*   

> Does that mean P4s are only "ordinary" Speedstep (or do they support frequency scaling at all? Does that mean I should not attempt to use frequency scaling on them?

 

P4 doesn't have Speedstep at all. It does not do freq or voltage scaling. P4_CLOCKMOD does what the option says - clock modulation. Which has a very limited use. A good read about that: http://www.codemonkey.org.uk/2009/01/18/forthcoming-p4clockmod/

P4-M is the one with Speedstep and it does both freq and voltage scaling.

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## Mad Merlin

Desktop P4s don't support speedstep in any form (enhanced or otherwise), so you'll likely just want to leave it at the maximum frequency.

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