scx_utils: Add EnergyModel (energy_model.rs). #1624
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Signed-off-by: Changwoo Min <[email protected]>
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Schedulers need to know the energy model of a system to make energy-aware
scheduling decisions. The EnergyModel (energy_model.rs) represents the energy
model of a system. It loads the energy model data from debugfs (typically at
/sys/kernel/debug/energy_model), so the kernel should support not only the
energy model (CONFIG_ENERGY_MODEL) but also debugfs.
A system's energy model (EnergyModel) consists of one or more performance
domains (PerfDomain). A group of CPUs belonging to the same performance domain
is frequency-scaled altogether (i.e., the same frequency domain), so it has
the same performance-power characteristics. The performance-power attributes
of a performance domain are represented by a collection of performance states
(PerfState). Each performance state includes
1) CPU frequency (kHz),
2) the cost of the transition,
3) performance scaled by 1024 against the highest performance of
the fastest CPU,
4) power consumption (mW), and
5) whether this state is power-inefficient or not.
Signed-off-by: Changwoo Min <[email protected]>
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The sched_ext schedulers [1] currently access the energy model through the debugfs to make energy-aware scheduling decisions [2]. The userspace part of a sched_ext scheduler feeds the necessary (post-processed) energy-model information to the BPF part of the scheduler. However, there is a limitation in the current debugfs support of the energy model. When the energy model is updated (em_dev_update_perf_domain), there is no way for the userspace part to know such changes (besides polling the debugfs files). Therefore, add inotify support (IN_MODIFY) when the energy model is updated. With this inotify support, the sched_ext scheduler can monitor the energy model change in userspace using the regular inotify interface and feed the updated energy model information to make energy-aware scheduling decisions. [1] https://lwn.net/Articles/922405/ [2] sched-ext/scx#1624 Signed-off-by: Changwoo Min <[email protected]>
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The sched_ext schedulers [1] currently access the energy model through the debugfs to make energy-aware scheduling decisions [2]. The userspace part of a sched_ext scheduler feeds the necessary (post-processed) energy-model information to the BPF part of the scheduler. However, there is a limitation in the current debugfs support of the energy model. When the energy model is updated (em_dev_update_perf_domain), there is no way for the userspace part to know such changes (besides polling the debugfs files). Therefore, add inotify support (IN_MODIFY) when the energy model is updated. With this inotify support, the directory of an updated performance domain (e.g., /sys/kernel/debug/energy_model/cpu0) and its parent directory (e.g., /sys/kernel/debug/energy_model) are inotified. Therefore, a sched_ext scheduler (or any userspace application) monitors the energy model change in userspace using the regular inotify interface. Note that accessing the energy model information from userspace has many advantages over other alternatives, especially adding new BPF kfuncs. The userspace has much more freedom than the BPF code (e.g., using external libraries and floating point arithmetics), which may be infeasible (if not impossible) in the BPF/kernel code. [1] https://lwn.net/Articles/922405/ [2] sched-ext/scx#1624 Signed-off-by: Changwoo Min <[email protected]>
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Schedulers need to know the energy model of a system to make energy-aware
scheduling decisions. The EnergyModel (energy_model.rs) represents the energy
model of a system. It loads the energy model data from debugfs (typically at
/sys/kernel/debug/energy_model), so the kernel should support not only the
energy model (CONFIG_ENERGY_MODEL) but also debugfs.
A system's energy model (EnergyModel) consists of one or more performance
domains (PerfDomain). A group of CPUs belonging to the same performance domain
is frequency-scaled altogether (i.e., the same frequency domain), so it has
the same performance-power characteristics. The performance-power attributes
of a performance domain are represented by a collection of performance states
(PerfState). Each performance state includes
the fastest CPU,