Messages in this thread Patch in this message | | | From | Morten Rasmussen <> | Subject | [RFC PATCH 01/16] sched: Documentation for scheduler energy cost model | Date | Fri, 23 May 2014 19:16:28 +0100 |
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This documentation patch provide a brief overview of the experimental scheduler energy costing model and associated data structures.
Signed-off-by: Morten Rasmussen <morten.rasmussen@arm.com> --- Documentation/scheduler/sched-energy.txt | 66 ++++++++++++++++++++++++++++++ 1 file changed, 66 insertions(+) create mode 100644 Documentation/scheduler/sched-energy.txt
diff --git a/Documentation/scheduler/sched-energy.txt b/Documentation/scheduler/sched-energy.txt new file mode 100644 index 0000000..c6896c0 --- /dev/null +++ b/Documentation/scheduler/sched-energy.txt @@ -0,0 +1,66 @@ +Energy cost model for energy-aware scheduling (EXPERIMENTAL) + +Introduction +============= +The basic energy model uses platform energy data stored in sched_energy data +structures attached to the sched_groups in the sched_domain hierarchy. The +energy cost model offers two function that can be used to guide scheduling +decisions: + +1. energy_diff_util(cpu, util, wakeups) +2. energy_diff_task(cpu, task) + +Both return the energy cost delta caused by adding/removing utilization or a +task to/from a specific cpu. + +CONFIG_SCHED_ENERGY needs to be defined in Kconfig to enable the energy cost +model and associated data structures. + +The basic algorithm +==================== +The basic idea is to determine the energy cost at each level in sched_domain +hierarchy based on utilization: + + for_each_domain(cpu, sd) { + sg = sched_group_of(cpu) + energy_before = curr_util(sg) * busy_power(sg) + + 1-curr_util(sg) * idle_power(sg) + energy_after = new_util(sg) * busy_power(sg) + + 1-new_util(sg) * idle_power(sg) + + new_util(sg) * task_wakeups + * wakeup_energy(sg) + energy_diff += energy_before - energy_after + } + + return energy_diff + +Platform energy data +===================== +struct sched_energy has the following members: + +cap_states: + List of struct capacity_state representing the supported capacity states + (P-states). struct capacity_state has two members: cap and power, which + represents the compute capacity and the busy power of the state. The + list must ordered by capacity low->high. + +nr_cap_states: + Number of capacity states in cap_states. + +max_capacity: + The highest capacity supported by any of the capacity states in + cap_states. + +idle_power: + Idle power consumption. Will be extended to support multiple C-states + later. + +wakeup_energy: + Energy cost of wakeup/power-down cycle for the sched_group which this is + attached to. Will be extended to support different costs for different + C-states later. + +There are no unit requirements for the energy cost data. Data can be normalized +with any reference, however, the normalization must be consistent across all +energy cost data. That is, one bogo-joule/watt must be same quantity for data, +but we don't care what it is. -- 1.7.9.5
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