diff options
Diffstat (limited to 'Documentation/cpu-freq/governors.txt')
| -rw-r--r-- | Documentation/cpu-freq/governors.txt | 72 |
1 files changed, 64 insertions, 8 deletions
diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt index 5b0cfa67aff..77ec21574fb 100644 --- a/Documentation/cpu-freq/governors.txt +++ b/Documentation/cpu-freq/governors.txt @@ -40,7 +40,7 @@ Most cpufreq drivers (in fact, all except one, longrun) or even most cpu frequency scaling algorithms only offer the CPU to be set to one frequency. In order to offer dynamic frequency scaling, the cpufreq core must be able to tell these drivers of a "target frequency". So -these specific drivers will be transformed to offer a "->target" +these specific drivers will be transformed to offer a "->target/target_index" call instead of the existing "->setpolicy" call. For "longrun", all stays the same, though. @@ -71,7 +71,7 @@ CPU can be set to switch independently | CPU can only be set / the limits of policy->{min,max} / \ / \ - Using the ->setpolicy call, Using the ->target call, + Using the ->setpolicy call, Using the ->target/target_index call, the limits and the the frequency closest "policy" is set. to target_freq is set. It is assured that it @@ -117,16 +117,34 @@ accessible parameters: sampling_rate: measured in uS (10^-6 seconds), this is how often you want the kernel to look at the CPU usage and to make decisions on what to do about the frequency. Typically this is set to values of -around '10000' or more. - -show_sampling_rate_(min|max): the minimum and maximum sampling rates -available that you may set 'sampling_rate' to. +around '10000' or more. It's default value is (cmp. with users-guide.txt): +transition_latency * 1000 +Be aware that transition latency is in ns and sampling_rate is in us, so you +get the same sysfs value by default. +Sampling rate should always get adjusted considering the transition latency +To set the sampling rate 750 times as high as the transition latency +in the bash (as said, 1000 is default), do: +echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) \ + >ondemand/sampling_rate + +sampling_rate_min: +The sampling rate is limited by the HW transition latency: +transition_latency * 100 +Or by kernel restrictions: +If CONFIG_NO_HZ_COMMON is set, the limit is 10ms fixed. +If CONFIG_NO_HZ_COMMON is not set or nohz=off boot parameter is used, the +limits depend on the CONFIG_HZ option: +HZ=1000: min=20000us (20ms) +HZ=250: min=80000us (80ms) +HZ=100: min=200000us (200ms) +The highest value of kernel and HW latency restrictions is shown and +used as the minimum sampling rate. up_threshold: defines what the average CPU usage between the samplings of 'sampling_rate' needs to be for the kernel to make a decision on whether it should increase the frequency. For example when it is set -to its default value of '80' it means that between the checking -intervals the CPU needs to be on average more than 80% in use to then +to its default value of '95' it means that between the checking +intervals the CPU needs to be on average more than 95% in use to then decide that the CPU frequency needs to be increased. ignore_nice_load: this parameter takes a value of '0' or '1'. When @@ -138,6 +156,38 @@ intensive calculation on your laptop that you do not care how long it takes to complete as you can 'nice' it and prevent it from taking part in the deciding process of whether to increase your CPU frequency. +sampling_down_factor: this parameter controls the rate at which the +kernel makes a decision on when to decrease the frequency while running +at top speed. When set to 1 (the default) decisions to reevaluate load +are made at the same interval regardless of current clock speed. But +when set to greater than 1 (e.g. 100) it acts as a multiplier for the +scheduling interval for reevaluating load when the CPU is at its top +speed due to high load. This improves performance by reducing the overhead +of load evaluation and helping the CPU stay at its top speed when truly +busy, rather than shifting back and forth in speed. This tunable has no +effect on behavior at lower speeds/lower CPU loads. + +powersave_bias: this parameter takes a value between 0 to 1000. It +defines the percentage (times 10) value of the target frequency that +will be shaved off of the target. For example, when set to 100 -- 10%, +when ondemand governor would have targeted 1000 MHz, it will target +1000 MHz - (10% of 1000 MHz) = 900 MHz instead. This is set to 0 +(disabled) by default. +When AMD frequency sensitivity powersave bias driver -- +drivers/cpufreq/amd_freq_sensitivity.c is loaded, this parameter +defines the workload frequency sensitivity threshold in which a lower +frequency is chosen instead of ondemand governor's original target. +The frequency sensitivity is a hardware reported (on AMD Family 16h +Processors and above) value between 0 to 100% that tells software how +the performance of the workload running on a CPU will change when +frequency changes. A workload with sensitivity of 0% (memory/IO-bound) +will not perform any better on higher core frequency, whereas a +workload with sensitivity of 100% (CPU-bound) will perform better +higher the frequency. When the driver is loaded, this is set to 400 +by default -- for CPUs running workloads with sensitivity value below +40%, a lower frequency is chosen. Unloading the driver or writing 0 +will disable this feature. + 2.5 Conservative ---------------- @@ -162,6 +212,12 @@ governor but for the opposite direction. For example when set to its default value of '20' it means that if the CPU usage needs to be below 20% between samples to have the frequency decreased. +sampling_down_factor: similar functionality as in "ondemand" governor. +But in "conservative", it controls the rate at which the kernel makes +a decision on when to decrease the frequency while running in any +speed. Load for frequency increase is still evaluated every +sampling rate. + 3. The Governor Interface in the CPUfreq Core ============================================= |