Further testing of power management

[Bruno Ducrot]

On Sun, Apr 10, 2005 at 02:02:20PM -0700, Nate Lawson wrote:
> Kevin Oberman wrote:
> >Nate,
> >
> >I finally had time to do some careful testing of power management on
> >-current. All testing was done on my IBM T30 with a 1.8 GHz P4-M
> >Processor. CPU load was generated by the use of md5 on a long gatch of
> >zeros. (As you suggested.)
> >
> >First, on power dissipation, while the use of TCC and adjusting actual
> >CPU frequency causes very predictable compute performance. They do not
> >produce the expected matching power dissipation.
> >
> >Here is a chart of the CPU temperature against the value of
> >dev.cpu.0.freq. The third column list the actual clock frequency that
> >the CPU is using. The T30 supports only 2 frequencies, 1.8 GHz and 1.2
> >GHz.
> >
> >dev.cpu.0.freq	Temperature	CPU Clock
> >1800		>_PSV		1800
> >1575		>_PSV		1800
> >1350		85		1800
> >1200		73		1200
> >1125		82		1800
> >1050		69		1200
> >900		77		1800
> >750		64		1200
> >675		72		1800
> >600		62		1200
> >450		66		1800
> >300		56		1200
> >225		61		1800
> >150		54		1200
> >
> >As you can see, lowering the CPU cock speed is much more effective in
> >reducing CPU heat (and battery drain) than doing it with TCC. I can get
> >much better performance with lower battery consumption at 1200 MHz than
> >at 900 MHz. Clearly, if both clock and TCC can provide identical
> >performance, you want the slower clock. This is backwards from how it is
> >now running as both 900 MHZ and 450 MHz can be achieved at either 1800
> >MHZ or 1200MHz clocking, but are clocked at 1800 MHz.
> 
> Thanks for your testing.  I agree that settings like the 900 mhz value 
> don't make sense to use when the 1050 value has lower heat.  Do you have 
> known values for power consumption (sysctl dev.cpu.0.freq_levels, look 
> for the second number after the /)?  Unknown values are marked -1.  Is 
> the power consumption for 900 higher than 1050?  If so, we could add a 
> test that compares power consumption and discards levels that have lower 
> frequencies but higher power consumption than their neighbors.

What strange is that we got 900 = 1800 * .50, but I would expect
900 = 1200 * .75 since 0.75 is valid.

-- 
Bruno Ducrot

--  Which is worse:  ignorance or apathy?
--  Don't know.  Don't care.