Lines Matching +full:waking +full:- +full:up
6 ---------------
25 please refer to its documentation (see Documentation/power/energy-model.rst).
29 -----------------------------
32 - energy = [joule] (resource like a battery on powered devices)
33 - power = energy/time = [joule/second] = [watt]
39 --------------------
45 -----------
49 optimization objective to the current performance-only objective for the
50 scheduler. This alternative considers two objectives: energy-efficiency and
54 implications of its decisions rather than blindly applying energy-saving
60 for the scheduler to decide where a task should run (during wake-up), the EM
69 -----------------------
76 tasks and CPUs computed by the Per-Entity Load Tracking (PELT) mechanism. Thanks
79 energy trade-offs. The capacity of CPUs is provided via arch-specific code
84 per 'performance domain' in the system (see Documentation/power/energy-model.rst
88 scheduling domains are built, or re-built. For each root domain (rd), the
90 the current rd->span. Each node in the list contains a pointer to a struct
103 PDs: |--pd0--|--pd4--|---pd8---|
104 RDs: |----rd1----|-----rd2-----|
110 present in the linked list '->pd' attached to each of them:
112 * rd1->pd: pd0 -> pd4
113 * rd2->pd: pd4 -> pd8
128 4. Energy-Aware task placement
129 ------------------------------
131 EAS overrides the CFS task wake-up balancing code. It uses the EM of the
132 platform and the PELT signals to choose an energy-efficient target CPU during
133 wake-up balance. When EAS is enabled, select_task_rq_fair() calls
135 for the CPU with the highest spare capacity (CPU capacity - CPU utilization) in
142 energy consumed by the system if the waking task was migrated. compute_energy()
148 An example of energy-optimized task placement decision is detailed below.
159 below. CPUs 0-3 have a util_avg of 400, 100, 600 and 500 respectively
166 1024 - - - - - - - Energy Model
167 +-----------+-------------+
169 768 ============= +-----+-----+------+------+
171 +-----+-----+------+------+
172 512 =========== - ##- - - - - | 170 | 50 | 512 | 400 |
174 341 -PP - - - - ## ## | 512 | 300 | 1024 | 1700 |
175 PP ## ## +-----+-----+------+------+
176 170 -## - - - - ## ##
178 ------------ -------------
181 Current OPP: ===== Other OPP: - - - util_avg (100 each): ##
194 1024 - - - - - - -
200 512 - - - - - - - ##- - - - - * CPU3: 500 / 768 * 800 = 520
204 170 -## - - PP- ## ##
206 ------------ -------------
212 1024 - - - - - - -
218 512 - - - - - - - ##- - -PP - * CPU3: 700 / 768 * 800 = 729
222 170 -## - - - - ## ##
224 ------------ -------------
230 1024 - - - - - - -
236 512 =========== - ##- - - - - * CPU3: 500 / 768 * 800 = 520
238 341 -PP - - - - ## ##
240 170 -## - - - - ## ##
242 ------------ -------------
247 is be the best candidate from an energy-efficiency standpoint.
251 necessarily more energy-efficient than big CPUs. For some systems, the high OPPs
252 of the little CPUs can be less energy-efficient than the lowest OPPs of the
254 a specific point in time, a small task waking up at that moment could be better
258 And even in the case where all OPPs of the big CPUs are less energy-efficient
262 increase the cost of the tasks already running there. If the waking task is
272 CPUs of the system. Thanks to its EM-based design, EAS should cope with them
274 impact on throughput for high-utilization scenarios, EAS also implements another
275 mechanism called 'over-utilization'.
278 5. Over-utilization
279 -------------------
281 From a general standpoint, the use-cases where EAS can help the most are those
282 involving a light/medium CPU utilization. Whenever long CPU-bound tasks are
286 'over-utilized' as soon as they are used at more than 80% of their compute
287 capacity. As long as no CPUs are over-utilized in a root domain, load balancing
288 is disabled and EAS overridess the wake-up balancing code. EAS is likely to load
290 done without harming throughput. So, the load-balancer is disabled to prevent
291 it from breaking the energy-efficient task placement found by EAS. It is safe to
301 regularly and balancing at wake-up is sufficient.
305 is raised for the entire root domain, EAS is disabled, and the load-balancer is
306 re-enabled. By doing so, the scheduler falls back onto load-based algorithms for
307 wake-up and load balance under CPU-bound conditions. This provides a better
318 ----------------------------------------
325 6.1 - Asymmetric CPU topology
330 asymmetric CPU topologies for now. This requirement is checked at run-time by
334 See Documentation/scheduler/sched-capacity.rst for requirements to be met for this
342 6.2 - Energy Model presence
348 independent EM framework in Documentation/power/energy-model.rst.
350 Please also note that the scheduling domains need to be re-built after the
356 in milli-Watts or in an 'abstract scale'.
359 6.3 - Energy Model complexity
367 6.4 - Schedutil governor
385 6.5 Scale-invariant utilization signals
389 states, EAS needs frequency-invariant and CPU-invariant PELT signals. These can
390 be obtained using the architecture-defined arch_scale{cpu,freq}_capacity()
402 CPUs, which can actually be counter-productive for both performance and energy.