wok-next view linux/description.linux-cpufreq.txt @ rev 19925
libftdi: update bdeps
| author | Pascal Bellard <pascal.bellard@slitaz.org> |
|---|---|
| date | Sat Oct 14 23:27:36 2017 +0200 (2017-10-14) |
| parents | 119e586fb823 |
| children |
line source
1 CPU Frequency scaling
3 CPU Frequency scaling allows you to change the clock speed of CPUs on the fly.
4 This is a nice method to save power, because the lower the CPU clock speed, the
5 less power the CPU consumes.
7 Note that this driver doesn't automatically change the CPU clock speed, you
8 need to either enable a dynamic cpufreq governor (see below) after boot, or use
9 a userspace tool.
11 * 'performance' governor
12 This cpufreq governor sets the frequency statically to the highest
13 available CPU frequency.
14 * 'powersave' governor
15 This cpufreq governor sets the frequency statically to the lowest available
16 CPU frequency.
17 * 'userspace' governor for userspace frequency scaling
18 Enable this cpufreq governor when you either want to set the CPU frequency
19 manually or when a userspace program shall be able to set the CPU
20 dynamically, like on LART <http://www.lartmaker.nl/>.
21 * 'ondemand' cpufreq policy governor
22 'ondemand' - This driver adds a dynamic cpufreq policy governor. The
23 governor does a periodic polling and changes frequency based on the CPU
24 utilization. The support for this governor depends on CPU capability to do
25 fast frequency switching (i.e, very low latency frequency transitions).
26 * 'conservative' cpufreq governor
27 'conservative' - this driver is rather similar to the 'ondemand' governor
28 both in its source code and its purpose, the difference is its optimisation
29 for better suitability in a battery powered environment. The frequency is
30 gracefully increased and decreased rather than jumping to 100% when speed
31 is required.
32 If you have a desktop machine then you should really be considering the
33 'ondemand' governor instead, however if you are using a laptop, PDA or even
34 an AMD64 based computer (due to the unacceptable step-by-step latency
35 issues between the minimum and maximum frequency transitions in the CPU)
36 you will probably want to use this governor.
37 * 'schedutil' cpufreq policy governor
38 This governor makes decisions based on the utilization data provided by the
39 scheduler. It sets the CPU frequency to be proportional to the
40 utilization/capacity ratio coming from the scheduler. If the utilization is
41 frequency-invariant, the new frequency is also proportional to the maximum
42 available frequency. If that is not the case, it is proportional to the
43 current frequency of the CPU. The frequency tipping point is at
44 utilization/capacity equal to 80% in both cases.