wok-next diff linux-cpufreq/description.txt @ rev 19618
memtest: update for GCC5
author | Pascal Bellard <pascal.bellard@slitaz.org> |
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date | Mon Feb 06 18:15:00 2017 +0100 (2017-02-06) |
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1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000 1.2 +++ b/linux-cpufreq/description.txt Mon Feb 06 18:15:00 2017 +0100 1.3 @@ -0,0 +1,44 @@ 1.4 +CPU Frequency scaling 1.5 + 1.6 +CPU Frequency scaling allows you to change the clock speed of CPUs on the fly. 1.7 +This is a nice method to save power, because the lower the CPU clock speed, the 1.8 +less power the CPU consumes. 1.9 + 1.10 +Note that this driver doesn't automatically change the CPU clock speed, you 1.11 +need to either enable a dynamic cpufreq governor (see below) after boot, or use 1.12 +a userspace tool. 1.13 + 1.14 + * 'performance' governor 1.15 + This cpufreq governor sets the frequency statically to the highest 1.16 + available CPU frequency. 1.17 + * 'powersave' governor 1.18 + This cpufreq governor sets the frequency statically to the lowest available 1.19 + CPU frequency. 1.20 + * 'userspace' governor for userspace frequency scaling 1.21 + Enable this cpufreq governor when you either want to set the CPU frequency 1.22 + manually or when a userspace program shall be able to set the CPU 1.23 + dynamically, like on LART <http://www.lartmaker.nl/>. 1.24 + * 'ondemand' cpufreq policy governor 1.25 + 'ondemand' - This driver adds a dynamic cpufreq policy governor. The 1.26 + governor does a periodic polling and changes frequency based on the CPU 1.27 + utilization. The support for this governor depends on CPU capability to do 1.28 + fast frequency switching (i.e, very low latency frequency transitions). 1.29 + * 'conservative' cpufreq governor 1.30 + 'conservative' - this driver is rather similar to the 'ondemand' governor 1.31 + both in its source code and its purpose, the difference is its optimisation 1.32 + for better suitability in a battery powered environment. The frequency is 1.33 + gracefully increased and decreased rather than jumping to 100% when speed 1.34 + is required. 1.35 + If you have a desktop machine then you should really be considering the 1.36 + 'ondemand' governor instead, however if you are using a laptop, PDA or even 1.37 + an AMD64 based computer (due to the unacceptable step-by-step latency 1.38 + issues between the minimum and maximum frequency transitions in the CPU) 1.39 + you will probably want to use this governor. 1.40 + * 'schedutil' cpufreq policy governor 1.41 + This governor makes decisions based on the utilization data provided by the 1.42 + scheduler. It sets the CPU frequency to be proportional to the 1.43 + utilization/capacity ratio coming from the scheduler. If the utilization is 1.44 + frequency-invariant, the new frequency is also proportional to the maximum 1.45 + available frequency. If that is not the case, it is proportional to the 1.46 + current frequency of the CPU. The frequency tipping point is at 1.47 + utilization/capacity equal to 80% in both cases.