Further testing of power management
ducrot at poupinou.org
Mon Apr 11 03:37:29 PDT 2005
On Sun, Apr 10, 2005 at 02:02:20PM -0700, Nate Lawson wrote:
> Kevin Oberman wrote:
> >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
> >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.
-- Which is worse: ignorance or apathy?
-- Don't know. Don't care.
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