Hi!
> >>>> Tested on Intel i7-3770 CPU @ 3.40GHz and on ARM quad core 1500MHz Krait
> >>>> (Android smartphone).
> >>>> Benchmarks on Intel i7 shows a performance improvement on low and medium
> >>>> work loads with lower power consumption. Specifics:
> >>>>
> >>>> Phoronix Linux Kernel Compilation 3.1:
> >>>> Time: -0.40%, energy: -0.07%
> >>>> Phoronix Apache:
> >>>> Time: -4.98%, energy: -2.35%
> >>>> Phoronix FFMPEG:
> >>>> Time: -6.29%, energy: -4.02%
> >>>
> >>> Hmm. Intel i7 should be race-to-idle machine. So basically rule like
> >>> if (load > 0) go to max frequency else go to lowest frequency would do
> >>> the right thing in your test, right?
> >>
> >> I don't think that "if (load > 0) go to max" will work even on i7.
> >> For low load this will have impact on energy consumption.
> >
> > Are you sure? CPU frequency should not matter on idle CPU.
>
> Even on a totally idle CPU there will be a small impact because of leakage
> current (thanks to Dirk Brandewie for this info).
Are you sure? IIRC Intel cpus will automatically lower CPU frequency
in deep C states..
> This simple test on a nearly idle system shows this:
>
> [root@albert cpufreq]# for CPUFREQ in
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do [ -f $CPUFREQ ] ||
> continue; echo -n performance > $CPUFREQ; done
> [root@albert cpufreq]#
> /home/stratosk/kernels/linux-pm/tools/power/x86/turbostat/turbostat -J sleep
> 20
> Core CPU Avg_MHz %Busy Bzy_MHz TSC_MHz SMI CPU%c1 CPU%c3
> CPU%c6 CPU%c7 CoreTmp PkgTmp Pkg%pc2 Pkg%pc3 Pkg%pc6 Pkg%pc7 Pkg_J
> Cor_J GFX_J time
> - - 2 0.06 2712 3392 0 0.30 0.00
> 99.63 0.00 34 34 8.09 0.00 81.94 0.00 380.41 14.51
> 1.64 20.00
> 0 0 0 0.02 1891 3392 0 0.09 0.00
> 99.88 0.00 34 34 8.09 0.00 81.94 0.00 380.41 14.51
> 1.64 20.00
> 0 4 1 0.04 3006 3392 0 0.07
> 1 1 1 0.04 2501 3392 0 0.62 0.00
> 99.33 0.00 34
> 1 5 0 0.01 2346 3392 0 0.66
> 2 2 0 0.01 1996 3392 0 0.44 0.00
> 99.55 0.00 34
> 2 6 4 0.18 2278 3392 0 0.26
> 3 3 5 0.15 3449 3392 0 0.07 0.01
> 99.77 0.00 34
> 3 7 0 0.01 1839 3392 0 0.21
> 20.000899 sec
> [root@albert cpufreq]# ^C
> [root@albert cpufreq]# for CPUFREQ in
> /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor; do [ -f $CPUFREQ ] ||
> continue; echo -n ondemand > $CPUFREQ; done
> [root@albert cpufreq]#
> /home/stratosk/kernels/linux-pm/tools/power/x86/turbostat/turbostat -J sleep
> 20
> Core CPU Avg_MHz %Busy Bzy_MHz TSC_MHz SMI CPU%c1 CPU%c3
> CPU%c6 CPU%c7 CoreTmp PkgTmp Pkg%pc2 Pkg%pc3 Pkg%pc6 Pkg%pc7 Pkg_J
> Cor_J GFX_J time
> - - 2 0.09 1693 3392 0 0.35 0.01
> 99.55 0.00 35 36 8.33 0.00 84.31 0.00 377.68 12.23
> 1.15 20.00
> 0 0 1 0.08 1603 3392 0 0.13 0.00
> 99.79 0.00 35 36 8.33 0.00 84.31 0.00 377.68 12.23
> 1.15 20.00
> 0 4 1 0.08 1646 3392 0 0.13
> 1 1 1 0.06 1647 3392 0 0.66 0.00
> 99.28 0.00 35
> 1 5 0 0.01 1611 3392 0 0.71
> 2 2 0 0.02 1617 3392 0 0.50 0.02
> 99.46 0.00 35
> 2 6 4 0.22 1764 3392 0 0.30
> 3 3 4 0.25 1701 3392 0 0.07 0.00
> 99.68 0.00 35
> 3 7 0 0.01 1602 3392 0 0.31
> 20.001580 sec
>
>
> So, for low loads the impact will be higher.
So it seems ondemand saves cca 1% of energy?
Best regards,
Pavel
--
(english) http://www.livejournal.com/~pavelmachek
(cesky, pictures)
http://atrey.karlin.mff.cuni.cz/~pavel/picture/horses/blog.html
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