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diff --git a/Documentation/cpu-freq/governors.txt b/Documentation/cpu-freq/governors.txt index e74d0a2..963a543 100644 --- a/Documentation/cpu-freq/governors.txt +++ b/Documentation/cpu-freq/governors.txt @@ -28,6 +28,7 @@ Contents: 2.3 Userspace 2.4 Ondemand 2.5 Conservative +2.6 Interactive 3. The Governor Interface in the CPUfreq Core @@ -193,6 +194,64 @@ 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. + +2.6 Interactive +--------------- + +The CPUfreq governor "interactive" is designed for latency-sensitive, +interactive workloads. This governor sets the CPU speed depending on +usage, similar to "ondemand" and "conservative" governors. However, +the governor is more aggressive about scaling the CPU speed up in +response to CPU-intensive activity. + +Sampling the CPU load every X ms can lead to under-powering the CPU +for X ms, leading to dropped frames, stuttering UI, etc. Instead of +sampling the cpu at a specified rate, the interactive governor will +check whether to scale the cpu frequency up soon after coming out of +idle. When the cpu comes out of idle, a timer is configured to fire +within 1-2 ticks. If the cpu is very busy between exiting idle and +when the timer fires then we assume the cpu is underpowered and ramp +to MAX speed. + +If the cpu was not sufficiently busy to immediately ramp to MAX speed, +then governor evaluates the cpu load since the last speed adjustment, +choosing the highest value between that longer-term load or the +short-term load since idle exit to determine the cpu speed to ramp to. + +The tuneable values for this governor are: + +min_sample_time: The minimum amount of time to spend at the current +frequency before ramping down. This is to ensure that the governor has +seen enough historic cpu load data to determine the appropriate +workload. Default is 80000 uS. + +hispeed_freq: An intermediate "hi speed" at which to initially ramp +when CPU load hits the value specified in go_hispeed_load. If load +stays high for the amount of time specified in above_hispeed_delay, +then speed may be bumped higher. Default is maximum speed. + +go_hispeed_load: The CPU load at which to ramp to the intermediate "hi +speed". Default is 85%. + +above_hispeed_delay: Once speed is set to hispeed_freq, wait for this +long before bumping speed higher in response to continued high load. +Default is 20000 uS. + +timer_rate: Sample rate for reevaluating cpu load when the system is +not idle. Default is 20000 uS. + +input_boost: If non-zero, boost speed of all CPUs to hispeed_freq on +touchscreen activity. Default is 0. + +boost: If non-zero, immediately boost speed of all CPUs to at least +hispeed_freq until zero is written to this attribute. If zero, allow +CPU speeds to drop below hispeed_freq according to load as usual. + +boostpulse: Immediately boost speed of all CPUs to hispeed_freq for +min_sample_time, after which speeds are allowed to drop below +hispeed_freq according to load as usual. + + 3. The Governor Interface in the CPUfreq Core ============================================= |