scx_lavd: improve CPU frequency scaling #351
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added 6 commits
June 12, 2024 15:58
When a device is suspended and resumed, the suspended duration is added up to a task's runtime if the task was running on the CPU. After the resume, the task's runtime is incorrectly long and the scheduler starts to recognize the system is under heavy load. To avoid such problem, the suspended duration is measured and substracted from the task's runtime. Signed-off-by: Changwoo Min <[email protected]>
The periodic CPU utilization routine does a lot of other work now. So we rename LAVD_CPU_UTIL_INTERVAL_NS to LAVD_SYS_STAT_INTERVAL_NS. Signed-off-by: Changwoo Min <[email protected]>
Originally, do_update_sys_stat() simply calculated the system-wide CPU utilization. Over time, it has evolved to collect all kinds of system-wide, periodic statistics for decision-making, so it has become bulky. Now, it is time to refactor it for readability. This commit does not contain functional changes other than refactoring. Signed-off-by: Changwoo Min <[email protected]>
The old logic for CPU frequency scaling is that the task's CPU performance target (i.e., target CPU frequency) is checked every tick interval and updated immediately. Indeed, it samples and updates a performance target every tick interval. Ultimately, it fluctuates CPU frequency every tick interval, resulting in less steady performance. Now, we take a different strategy. The key idea is to increase the frequency as soon as possible when a task starts running for quick adoption to load spikes. However, if necessary, it decreases gradually every tick interval to avoid frequency fluctuations. In my testing, it shows more stable performance in many workloads (games, compilation). Signed-off-by: Changwoo Min <[email protected]>
Signed-off-by: Changwoo Min <[email protected]>
Signed-off-by: Changwoo Min <[email protected]>
htejun
approved these changes
Jun 13, 2024
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This PR includes the improvement of CPU frequency scaling in LAVD, in addition to some refactoring, clean-up, and documentation.
The old logic for CPU frequency scaling is that the task's CPU performance target (i.e., target CPU frequency) is checked every tick interval and updated immediately. Indeed, it samples and updates a performance target every tick interval. Ultimately, it fluctuates CPU frequency every tick interval, resulting in less steady performance.
Now, we take a different strategy. The key idea is to increase the frequency as soon as possible when a task starts running for quick adoption to load spikes. However, it decreases gradually every tick interval to avoid frequency fluctuations if necessary.
In my testing, it shows more stable performance in many workloads (games, compilation).