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Diffstat (limited to 'Documentation/admin-guide/pm/cpufreq.rst')
| -rw-r--r-- | Documentation/admin-guide/pm/cpufreq.rst | 43 |
1 files changed, 31 insertions, 12 deletions
diff --git a/Documentation/admin-guide/pm/cpufreq.rst b/Documentation/admin-guide/pm/cpufreq.rst index 6adb7988e0eb..2d74af7f0efe 100644 --- a/Documentation/admin-guide/pm/cpufreq.rst +++ b/Documentation/admin-guide/pm/cpufreq.rst @@ -231,7 +231,7 @@ are the following: present). The existence of the limit may be a result of some (often unintentional) - BIOS settings, restrictions coming from a service processor or another + BIOS settings, restrictions coming from a service processor or other BIOS/HW-based mechanisms. This does not cover ACPI thermal limitations which can be discovered @@ -248,6 +248,20 @@ are the following: If that frequency cannot be determined, this attribute should not be present. +``cpuinfo_avg_freq`` + An average frequency (in KHz) of all CPUs belonging to a given policy, + derived from a hardware provided feedback and reported on a time frame + spanning at most few milliseconds. + + This is expected to be based on the frequency the hardware actually runs + at and, as such, might require specialised hardware support (such as AMU + extension on ARM). If one cannot be determined, this attribute should + not be present. + + Note that failed attempt to retrieve current frequency for a given + CPU(s) will result in an appropriate error, i.e.: EAGAIN for CPU that + remains idle (raised on ARM). + ``cpuinfo_max_freq`` Maximum possible operating frequency the CPUs belonging to this policy can run at (in kHz). @@ -267,6 +281,10 @@ are the following: ``related_cpus`` List of all (online and offline) CPUs belonging to this policy. +``scaling_available_frequencies`` + List of available frequencies of the CPUs belonging to this policy + (in kHz). + ``scaling_available_governors`` List of ``CPUFreq`` scaling governors present in the kernel that can be attached to this policy or (if the |intel_pstate| scaling driver is @@ -289,7 +307,8 @@ are the following: Some architectures (e.g. ``x86``) may attempt to provide information more precisely reflecting the current CPU frequency through this attribute, but that still may not be the exact current CPU frequency as - seen by the hardware at the moment. + seen by the hardware at the moment. This behavior though, is only + available via c:macro:``CPUFREQ_ARCH_CUR_FREQ`` option. ``scaling_driver`` The scaling driver currently in use. @@ -421,8 +440,8 @@ This governor exposes only one tunable: ``rate_limit_us`` Minimum time (in microseconds) that has to pass between two consecutive - runs of governor computations (default: 1000 times the scaling driver's - transition latency). + runs of governor computations (default: 1.5 times the scaling driver's + transition latency or the maximum 2ms). The purpose of this tunable is to reduce the scheduler context overhead of the governor which might be excessive without it. @@ -470,17 +489,17 @@ This governor exposes the following tunables: This is how often the governor's worker routine should run, in microseconds. - Typically, it is set to values of the order of 10000 (10 ms). Its - default value is equal to the value of ``cpuinfo_transition_latency`` - for each policy this governor is attached to (but since the unit here - is greater by 1000, this means that the time represented by - ``sampling_rate`` is 1000 times greater than the transition latency by - default). + Typically, it is set to values of the order of 2000 (2 ms). Its + default value is to add a 50% breathing room + to ``cpuinfo_transition_latency`` on each policy this governor is + attached to. The minimum is typically the length of two scheduler + ticks. If this tunable is per-policy, the following shell command sets the time - represented by it to be 750 times as high as the transition latency:: + represented by it to be 1.5 times as high as the transition latency + (the default):: - # echo `$(($(cat cpuinfo_transition_latency) * 750 / 1000)) > ondemand/sampling_rate + # echo `$(($(cat cpuinfo_transition_latency) * 3 / 2))` > ondemand/sampling_rate ``up_threshold`` If the estimated CPU load is above this value (in percent), the governor |