On 21/07/2014 12:51 πμ, Pavel Machek wrote: > 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..
I'm sorry. I don't know further details about the leakage current in deeper 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? Yes, in this small test, on my nearly "idle" system. Stratos -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
