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Date: Fri, 23 May 2014 19:16:28 +0100
From: Morten Rasmussen <morten.rasmussen@....com>
To: linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
peterz@...radead.org, mingo@...nel.org
Cc: rjw@...ysocki.net, vincent.guittot@...aro.org,
daniel.lezcano@...aro.org, preeti@...ux.vnet.ibm.com,
dietmar.eggemann@....com
Subject: [RFC PATCH 01/16] sched: Documentation for scheduler energy cost model
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@....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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