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6 - Arjan van de Ven <arjan@linux.intel.com>
7 - Jacob Pan <jacob.jun.pan@linux.intel.com>
12 - Goals and Objectives
15 - Idle Injection
16 - Calibration
19 - Effectiveness and Limitations
20 - Power vs Performance
21 - Scalability
22 - Calibration
23 - Comparison with Alternative Techniques
26 - Generic Thermal Layer (sysfs)
27 - Kernel APIs (TBD)
36 level, and where active cooling is not preferred. Software managed
40 Currently, P-states, T-states (clock modulation), and CPU offlining
43 On Intel CPUs, C-states provide effective power reduction, but so far
47 is to achieve forced and controllable C-state residency.
51 shown over taking the CPU offline or modulating the CPU clock.
58 --------------
60 On modern Intel processors (Nehalem or later), package level C-state
71 closed-loop control system can be established that manages package
72 level C-state. The intel_powerclamp driver is conceived as such a
73 control system, where the target set point is a user-selected idle
75 between the actual package level C-state residency ratio and the target idle
78 Injection is controlled by high priority kernel threads, spawned for
82 clamping actions of controlled duty ratio and duration. Each per-CPU
89 Running as SCHED_FIFO and relatively high priority, also allows such
90 scheme to work for both preemptible and non-preemptible kernels.
123 hot-plug.
126 time is considered largely as a non-causal system where its behavior
127 cannot be based on the past or current input. Therefore, the
131 the next injection accordingly to avoid over/under correction.
136 PID-based thermal controller can use the powerclamp driver to
143 -----------
146 also true for the ability of a system to enter package level C-states.
218 non-intrusive to the scheduler or the IRQ core code.
222 ------------------
223 Per-CPU kernel threads are started/stopped upon receiving
235 -----------------------------
239 effectiveness. The extreme case would be doing a ping -f to generated
249 thus not able to enter package C- states at the expected ratio. But
255 -----------
265 counter summed over per CPU counting threads spawned for all running
281 actual and current idle percentage. This may not be the same value
282 set by the user in that current idle percentage depends on workload
284 cur_state returns value -1 instead of 0 which is to avoid confusing
289 - To inject 25% idle time::
291 $ sudo sh -c "echo 25 > /sys/class/thermal/cooling_device80/cur_state
313 3341 root -51 0 0 0 0 D 25 0.0 0:01.62 kidle_inject/0
314 3344 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/3
315 3342 root -51 0 0 0 0 D 25 0.0 0:01.61 kidle_inject/1
316 3343 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/2
325 certain temperature (below most active trip points).
337 The rightmost mask is for CPU 0-32.
343 to match the current implementation of powerclamp driver. Also doesn't