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This governor is designed for latency-sensitive workloads, such as interactive user interfaces. The interactive governor aims to be significantly more responsive to ramp CPU quickly up when CPU-intensive activity begins. Existing governors sample CPU load at a particular rate, typically every X ms. This can lead to under-powering UI threads for the period of time during which the user begins interacting with a previously-idle system until the next sample period happens. The 'interactive' governor uses a different approach. Instead of sampling the CPU at a specified rate, the 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 from exiting idle to 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 the 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. A realtime thread is used for scaling up, giving the remaining tasks the CPU performance benefit, unlike existing governors which are more likely to schedule rampup work to occur after your performance starved tasks have completed. The tuneables for this governor are: /sys/devices/system/cpu/cpufreq/interactive/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. /sys/devices/system/cpu/cpufreq/interactive/go_maxspeed_load The CPU load at which to ramp to max speed. Default is 85. Change-Id: Ib2b362607c62f7c56d35f44a9ef3280f98c17585 Signed-off-by: Mike Chan <mike@android.com> Signed-off-by: Todd Poynor <toddpoynor@google.com> Bug: 3152864 |
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