svga
syscall-user-dispatch
sysrq
+ thermal
thunderbolt
ufs
unicode
--- /dev/null
+=======================
+Intel Powerclamp Driver
+=======================
+
+By:
+ - Arjan van de Ven <arjan@linux.intel.com>
+ - Jacob Pan <jacob.jun.pan@linux.intel.com>
+
+.. Contents:
+
+ (*) Introduction
+ - Goals and Objectives
+
+ (*) Theory of Operation
+ - Idle Injection
+ - Calibration
+
+ (*) Performance Analysis
+ - Effectiveness and Limitations
+ - Power vs Performance
+ - Scalability
+ - Calibration
+ - Comparison with Alternative Techniques
+
+ (*) Usage and Interfaces
+ - Generic Thermal Layer (sysfs)
+ - Kernel APIs (TBD)
+
+INTRODUCTION
+============
+
+Consider the situation where a system’s power consumption must be
+reduced at runtime, due to power budget, thermal constraint, or noise
+level, and where active cooling is not preferred. Software managed
+passive power reduction must be performed to prevent the hardware
+actions that are designed for catastrophic scenarios.
+
+Currently, P-states, T-states (clock modulation), and CPU offlining
+are used for CPU throttling.
+
+On Intel CPUs, C-states provide effective power reduction, but so far
+they’re only used opportunistically, based on workload. With the
+development of intel_powerclamp driver, the method of synchronizing
+idle injection across all online CPU threads was introduced. The goal
+is to achieve forced and controllable C-state residency.
+
+Test/Analysis has been made in the areas of power, performance,
+scalability, and user experience. In many cases, clear advantage is
+shown over taking the CPU offline or modulating the CPU clock.
+
+
+THEORY OF OPERATION
+===================
+
+Idle Injection
+--------------
+
+On modern Intel processors (Nehalem or later), package level C-state
+residency is available in MSRs, thus also available to the kernel.
+
+These MSRs are::
+
+ #define MSR_PKG_C2_RESIDENCY 0x60D
+ #define MSR_PKG_C3_RESIDENCY 0x3F8
+ #define MSR_PKG_C6_RESIDENCY 0x3F9
+ #define MSR_PKG_C7_RESIDENCY 0x3FA
+
+If the kernel can also inject idle time to the system, then a
+closed-loop control system can be established that manages package
+level C-state. The intel_powerclamp driver is conceived as such a
+control system, where the target set point is a user-selected idle
+ratio (based on power reduction), and the error is the difference
+between the actual package level C-state residency ratio and the target idle
+ratio.
+
+Injection is controlled by high priority kernel threads, spawned for
+each online CPU.
+
+These kernel threads, with SCHED_FIFO class, are created to perform
+clamping actions of controlled duty ratio and duration. Each per-CPU
+thread synchronizes its idle time and duration, based on the rounding
+of jiffies, so accumulated errors can be prevented to avoid a jittery
+effect. Threads are also bound to the CPU such that they cannot be
+migrated, unless the CPU is taken offline. In this case, threads
+belong to the offlined CPUs will be terminated immediately.
+
+Running as SCHED_FIFO and relatively high priority, also allows such
+scheme to work for both preemptable and non-preemptable kernels.
+Alignment of idle time around jiffies ensures scalability for HZ
+values. This effect can be better visualized using a Perf timechart.
+The following diagram shows the behavior of kernel thread
+kidle_inject/cpu. During idle injection, it runs monitor/mwait idle
+for a given "duration", then relinquishes the CPU to other tasks,
+until the next time interval.
+
+The NOHZ schedule tick is disabled during idle time, but interrupts
+are not masked. Tests show that the extra wakeups from scheduler tick
+have a dramatic impact on the effectiveness of the powerclamp driver
+on large scale systems (Westmere system with 80 processors).
+
+::
+
+ CPU0
+ ____________ ____________
+ kidle_inject/0 | sleep | mwait | sleep |
+ _________| |________| |_______
+ duration
+ CPU1
+ ____________ ____________
+ kidle_inject/1 | sleep | mwait | sleep |
+ _________| |________| |_______
+ ^
+ |
+ |
+ roundup(jiffies, interval)
+
+Only one CPU is allowed to collect statistics and update global
+control parameters. This CPU is referred to as the controlling CPU in
+this document. The controlling CPU is elected at runtime, with a
+policy that favors BSP, taking into account the possibility of a CPU
+hot-plug.
+
+In terms of dynamics of the idle control system, package level idle
+time is considered largely as a non-causal system where its behavior
+cannot be based on the past or current input. Therefore, the
+intel_powerclamp driver attempts to enforce the desired idle time
+instantly as given input (target idle ratio). After injection,
+powerclamp monitors the actual idle for a given time window and adjust
+the next injection accordingly to avoid over/under correction.
+
+When used in a causal control system, such as a temperature control,
+it is up to the user of this driver to implement algorithms where
+past samples and outputs are included in the feedback. For example, a
+PID-based thermal controller can use the powerclamp driver to
+maintain a desired target temperature, based on integral and
+derivative gains of the past samples.
+
+
+
+Calibration
+-----------
+During scalability testing, it is observed that synchronized actions
+among CPUs become challenging as the number of cores grows. This is
+also true for the ability of a system to enter package level C-states.
+
+To make sure the intel_powerclamp driver scales well, online
+calibration is implemented. The goals for doing such a calibration
+are:
+
+a) determine the effective range of idle injection ratio
+b) determine the amount of compensation needed at each target ratio
+
+Compensation to each target ratio consists of two parts:
+
+ a) steady state error compensation
+ This is to offset the error occurring when the system can
+ enter idle without extra wakeups (such as external interrupts).
+
+ b) dynamic error compensation
+ When an excessive amount of wakeups occurs during idle, an
+ additional idle ratio can be added to quiet interrupts, by
+ slowing down CPU activities.
+
+A debugfs file is provided for the user to examine compensation
+progress and results, such as on a Westmere system::
+
+ [jacob@nex01 ~]$ cat
+ /sys/kernel/debug/intel_powerclamp/powerclamp_calib
+ controlling cpu: 0
+ pct confidence steady dynamic (compensation)
+ 0 0 0 0
+ 1 1 0 0
+ 2 1 1 0
+ 3 3 1 0
+ 4 3 1 0
+ 5 3 1 0
+ 6 3 1 0
+ 7 3 1 0
+ 8 3 1 0
+ ...
+ 30 3 2 0
+ 31 3 2 0
+ 32 3 1 0
+ 33 3 2 0
+ 34 3 1 0
+ 35 3 2 0
+ 36 3 1 0
+ 37 3 2 0
+ 38 3 1 0
+ 39 3 2 0
+ 40 3 3 0
+ 41 3 1 0
+ 42 3 2 0
+ 43 3 1 0
+ 44 3 1 0
+ 45 3 2 0
+ 46 3 3 0
+ 47 3 0 0
+ 48 3 2 0
+ 49 3 3 0
+
+Calibration occurs during runtime. No offline method is available.
+Steady state compensation is used only when confidence levels of all
+adjacent ratios have reached satisfactory level. A confidence level
+is accumulated based on clean data collected at runtime. Data
+collected during a period without extra interrupts is considered
+clean.
+
+To compensate for excessive amounts of wakeup during idle, additional
+idle time is injected when such a condition is detected. Currently,
+we have a simple algorithm to double the injection ratio. A possible
+enhancement might be to throttle the offending IRQ, such as delaying
+EOI for level triggered interrupts. But it is a challenge to be
+non-intrusive to the scheduler or the IRQ core code.
+
+
+CPU Online/Offline
+------------------
+Per-CPU kernel threads are started/stopped upon receiving
+notifications of CPU hotplug activities. The intel_powerclamp driver
+keeps track of clamping kernel threads, even after they are migrated
+to other CPUs, after a CPU offline event.
+
+
+Performance Analysis
+====================
+This section describes the general performance data collected on
+multiple systems, including Westmere (80P) and Ivy Bridge (4P, 8P).
+
+Effectiveness and Limitations
+-----------------------------
+The maximum range that idle injection is allowed is capped at 50
+percent. As mentioned earlier, since interrupts are allowed during
+forced idle time, excessive interrupts could result in less
+effectiveness. The extreme case would be doing a ping -f to generated
+flooded network interrupts without much CPU acknowledgement. In this
+case, little can be done from the idle injection threads. In most
+normal cases, such as scp a large file, applications can be throttled
+by the powerclamp driver, since slowing down the CPU also slows down
+network protocol processing, which in turn reduces interrupts.
+
+When control parameters change at runtime by the controlling CPU, it
+may take an additional period for the rest of the CPUs to catch up
+with the changes. During this time, idle injection is out of sync,
+thus not able to enter package C- states at the expected ratio. But
+this effect is minor, in that in most cases change to the target
+ratio is updated much less frequently than the idle injection
+frequency.
+
+Scalability
+-----------
+Tests also show a minor, but measurable, difference between the 4P/8P
+Ivy Bridge system and the 80P Westmere server under 50% idle ratio.
+More compensation is needed on Westmere for the same amount of
+target idle ratio. The compensation also increases as the idle ratio
+gets larger. The above reason constitutes the need for the
+calibration code.
+
+On the IVB 8P system, compared to an offline CPU, powerclamp can
+achieve up to 40% better performance per watt. (measured by a spin
+counter summed over per CPU counting threads spawned for all running
+CPUs).
+
+Usage and Interfaces
+====================
+The powerclamp driver is registered to the generic thermal layer as a
+cooling device. Currently, it’s not bound to any thermal zones::
+
+ jacob@chromoly:/sys/class/thermal/cooling_device14$ grep . *
+ cur_state:0
+ max_state:50
+ type:intel_powerclamp
+
+cur_state allows user to set the desired idle percentage. Writing 0 to
+cur_state will stop idle injection. Writing a value between 1 and
+max_state will start the idle injection. Reading cur_state returns the
+actual and current idle percentage. This may not be the same value
+set by the user in that current idle percentage depends on workload
+and includes natural idle. When idle injection is disabled, reading
+cur_state returns value -1 instead of 0 which is to avoid confusing
+100% busy state with the disabled state.
+
+Example usage:
+- To inject 25% idle time::
+
+ $ sudo sh -c "echo 25 > /sys/class/thermal/cooling_device80/cur_state
+
+If the system is not busy and has more than 25% idle time already,
+then the powerclamp driver will not start idle injection. Using Top
+will not show idle injection kernel threads.
+
+If the system is busy (spin test below) and has less than 25% natural
+idle time, powerclamp kernel threads will do idle injection. Forced
+idle time is accounted as normal idle in that common code path is
+taken as the idle task.
+
+In this example, 24.1% idle is shown. This helps the system admin or
+user determine the cause of slowdown, when a powerclamp driver is in action::
+
+
+ Tasks: 197 total, 1 running, 196 sleeping, 0 stopped, 0 zombie
+ Cpu(s): 71.2%us, 4.7%sy, 0.0%ni, 24.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
+ Mem: 3943228k total, 1689632k used, 2253596k free, 74960k buffers
+ Swap: 4087804k total, 0k used, 4087804k free, 945336k cached
+
+ PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
+ 3352 jacob 20 0 262m 644 428 S 286 0.0 0:17.16 spin
+ 3341 root -51 0 0 0 0 D 25 0.0 0:01.62 kidle_inject/0
+ 3344 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/3
+ 3342 root -51 0 0 0 0 D 25 0.0 0:01.61 kidle_inject/1
+ 3343 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/2
+ 2935 jacob 20 0 696m 125m 35m S 5 3.3 0:31.11 firefox
+ 1546 root 20 0 158m 20m 6640 S 3 0.5 0:26.97 Xorg
+ 2100 jacob 20 0 1223m 88m 30m S 3 2.3 0:23.68 compiz
+
+Tests have shown that by using the powerclamp driver as a cooling
+device, a PID based userspace thermal controller can manage to
+control CPU temperature effectively, when no other thermal influence
+is added. For example, a UltraBook user can compile the kernel under
+certain temperature (below most active trip points).
exynos_thermal
exynos_thermal_emulation
- intel_powerclamp
nouveau_thermal
x86_pkg_temperature_thermal
intel_dptf
+++ /dev/null
-=======================
-Intel Powerclamp Driver
-=======================
-
-By:
- - Arjan van de Ven <arjan@linux.intel.com>
- - Jacob Pan <jacob.jun.pan@linux.intel.com>
-
-.. Contents:
-
- (*) Introduction
- - Goals and Objectives
-
- (*) Theory of Operation
- - Idle Injection
- - Calibration
-
- (*) Performance Analysis
- - Effectiveness and Limitations
- - Power vs Performance
- - Scalability
- - Calibration
- - Comparison with Alternative Techniques
-
- (*) Usage and Interfaces
- - Generic Thermal Layer (sysfs)
- - Kernel APIs (TBD)
-
-INTRODUCTION
-============
-
-Consider the situation where a system’s power consumption must be
-reduced at runtime, due to power budget, thermal constraint, or noise
-level, and where active cooling is not preferred. Software managed
-passive power reduction must be performed to prevent the hardware
-actions that are designed for catastrophic scenarios.
-
-Currently, P-states, T-states (clock modulation), and CPU offlining
-are used for CPU throttling.
-
-On Intel CPUs, C-states provide effective power reduction, but so far
-they’re only used opportunistically, based on workload. With the
-development of intel_powerclamp driver, the method of synchronizing
-idle injection across all online CPU threads was introduced. The goal
-is to achieve forced and controllable C-state residency.
-
-Test/Analysis has been made in the areas of power, performance,
-scalability, and user experience. In many cases, clear advantage is
-shown over taking the CPU offline or modulating the CPU clock.
-
-
-THEORY OF OPERATION
-===================
-
-Idle Injection
---------------
-
-On modern Intel processors (Nehalem or later), package level C-state
-residency is available in MSRs, thus also available to the kernel.
-
-These MSRs are::
-
- #define MSR_PKG_C2_RESIDENCY 0x60D
- #define MSR_PKG_C3_RESIDENCY 0x3F8
- #define MSR_PKG_C6_RESIDENCY 0x3F9
- #define MSR_PKG_C7_RESIDENCY 0x3FA
-
-If the kernel can also inject idle time to the system, then a
-closed-loop control system can be established that manages package
-level C-state. The intel_powerclamp driver is conceived as such a
-control system, where the target set point is a user-selected idle
-ratio (based on power reduction), and the error is the difference
-between the actual package level C-state residency ratio and the target idle
-ratio.
-
-Injection is controlled by high priority kernel threads, spawned for
-each online CPU.
-
-These kernel threads, with SCHED_FIFO class, are created to perform
-clamping actions of controlled duty ratio and duration. Each per-CPU
-thread synchronizes its idle time and duration, based on the rounding
-of jiffies, so accumulated errors can be prevented to avoid a jittery
-effect. Threads are also bound to the CPU such that they cannot be
-migrated, unless the CPU is taken offline. In this case, threads
-belong to the offlined CPUs will be terminated immediately.
-
-Running as SCHED_FIFO and relatively high priority, also allows such
-scheme to work for both preemptable and non-preemptable kernels.
-Alignment of idle time around jiffies ensures scalability for HZ
-values. This effect can be better visualized using a Perf timechart.
-The following diagram shows the behavior of kernel thread
-kidle_inject/cpu. During idle injection, it runs monitor/mwait idle
-for a given "duration", then relinquishes the CPU to other tasks,
-until the next time interval.
-
-The NOHZ schedule tick is disabled during idle time, but interrupts
-are not masked. Tests show that the extra wakeups from scheduler tick
-have a dramatic impact on the effectiveness of the powerclamp driver
-on large scale systems (Westmere system with 80 processors).
-
-::
-
- CPU0
- ____________ ____________
- kidle_inject/0 | sleep | mwait | sleep |
- _________| |________| |_______
- duration
- CPU1
- ____________ ____________
- kidle_inject/1 | sleep | mwait | sleep |
- _________| |________| |_______
- ^
- |
- |
- roundup(jiffies, interval)
-
-Only one CPU is allowed to collect statistics and update global
-control parameters. This CPU is referred to as the controlling CPU in
-this document. The controlling CPU is elected at runtime, with a
-policy that favors BSP, taking into account the possibility of a CPU
-hot-plug.
-
-In terms of dynamics of the idle control system, package level idle
-time is considered largely as a non-causal system where its behavior
-cannot be based on the past or current input. Therefore, the
-intel_powerclamp driver attempts to enforce the desired idle time
-instantly as given input (target idle ratio). After injection,
-powerclamp monitors the actual idle for a given time window and adjust
-the next injection accordingly to avoid over/under correction.
-
-When used in a causal control system, such as a temperature control,
-it is up to the user of this driver to implement algorithms where
-past samples and outputs are included in the feedback. For example, a
-PID-based thermal controller can use the powerclamp driver to
-maintain a desired target temperature, based on integral and
-derivative gains of the past samples.
-
-
-
-Calibration
------------
-During scalability testing, it is observed that synchronized actions
-among CPUs become challenging as the number of cores grows. This is
-also true for the ability of a system to enter package level C-states.
-
-To make sure the intel_powerclamp driver scales well, online
-calibration is implemented. The goals for doing such a calibration
-are:
-
-a) determine the effective range of idle injection ratio
-b) determine the amount of compensation needed at each target ratio
-
-Compensation to each target ratio consists of two parts:
-
- a) steady state error compensation
- This is to offset the error occurring when the system can
- enter idle without extra wakeups (such as external interrupts).
-
- b) dynamic error compensation
- When an excessive amount of wakeups occurs during idle, an
- additional idle ratio can be added to quiet interrupts, by
- slowing down CPU activities.
-
-A debugfs file is provided for the user to examine compensation
-progress and results, such as on a Westmere system::
-
- [jacob@nex01 ~]$ cat
- /sys/kernel/debug/intel_powerclamp/powerclamp_calib
- controlling cpu: 0
- pct confidence steady dynamic (compensation)
- 0 0 0 0
- 1 1 0 0
- 2 1 1 0
- 3 3 1 0
- 4 3 1 0
- 5 3 1 0
- 6 3 1 0
- 7 3 1 0
- 8 3 1 0
- ...
- 30 3 2 0
- 31 3 2 0
- 32 3 1 0
- 33 3 2 0
- 34 3 1 0
- 35 3 2 0
- 36 3 1 0
- 37 3 2 0
- 38 3 1 0
- 39 3 2 0
- 40 3 3 0
- 41 3 1 0
- 42 3 2 0
- 43 3 1 0
- 44 3 1 0
- 45 3 2 0
- 46 3 3 0
- 47 3 0 0
- 48 3 2 0
- 49 3 3 0
-
-Calibration occurs during runtime. No offline method is available.
-Steady state compensation is used only when confidence levels of all
-adjacent ratios have reached satisfactory level. A confidence level
-is accumulated based on clean data collected at runtime. Data
-collected during a period without extra interrupts is considered
-clean.
-
-To compensate for excessive amounts of wakeup during idle, additional
-idle time is injected when such a condition is detected. Currently,
-we have a simple algorithm to double the injection ratio. A possible
-enhancement might be to throttle the offending IRQ, such as delaying
-EOI for level triggered interrupts. But it is a challenge to be
-non-intrusive to the scheduler or the IRQ core code.
-
-
-CPU Online/Offline
-------------------
-Per-CPU kernel threads are started/stopped upon receiving
-notifications of CPU hotplug activities. The intel_powerclamp driver
-keeps track of clamping kernel threads, even after they are migrated
-to other CPUs, after a CPU offline event.
-
-
-Performance Analysis
-====================
-This section describes the general performance data collected on
-multiple systems, including Westmere (80P) and Ivy Bridge (4P, 8P).
-
-Effectiveness and Limitations
------------------------------
-The maximum range that idle injection is allowed is capped at 50
-percent. As mentioned earlier, since interrupts are allowed during
-forced idle time, excessive interrupts could result in less
-effectiveness. The extreme case would be doing a ping -f to generated
-flooded network interrupts without much CPU acknowledgement. In this
-case, little can be done from the idle injection threads. In most
-normal cases, such as scp a large file, applications can be throttled
-by the powerclamp driver, since slowing down the CPU also slows down
-network protocol processing, which in turn reduces interrupts.
-
-When control parameters change at runtime by the controlling CPU, it
-may take an additional period for the rest of the CPUs to catch up
-with the changes. During this time, idle injection is out of sync,
-thus not able to enter package C- states at the expected ratio. But
-this effect is minor, in that in most cases change to the target
-ratio is updated much less frequently than the idle injection
-frequency.
-
-Scalability
------------
-Tests also show a minor, but measurable, difference between the 4P/8P
-Ivy Bridge system and the 80P Westmere server under 50% idle ratio.
-More compensation is needed on Westmere for the same amount of
-target idle ratio. The compensation also increases as the idle ratio
-gets larger. The above reason constitutes the need for the
-calibration code.
-
-On the IVB 8P system, compared to an offline CPU, powerclamp can
-achieve up to 40% better performance per watt. (measured by a spin
-counter summed over per CPU counting threads spawned for all running
-CPUs).
-
-Usage and Interfaces
-====================
-The powerclamp driver is registered to the generic thermal layer as a
-cooling device. Currently, it’s not bound to any thermal zones::
-
- jacob@chromoly:/sys/class/thermal/cooling_device14$ grep . *
- cur_state:0
- max_state:50
- type:intel_powerclamp
-
-cur_state allows user to set the desired idle percentage. Writing 0 to
-cur_state will stop idle injection. Writing a value between 1 and
-max_state will start the idle injection. Reading cur_state returns the
-actual and current idle percentage. This may not be the same value
-set by the user in that current idle percentage depends on workload
-and includes natural idle. When idle injection is disabled, reading
-cur_state returns value -1 instead of 0 which is to avoid confusing
-100% busy state with the disabled state.
-
-Example usage:
-- To inject 25% idle time::
-
- $ sudo sh -c "echo 25 > /sys/class/thermal/cooling_device80/cur_state
-
-If the system is not busy and has more than 25% idle time already,
-then the powerclamp driver will not start idle injection. Using Top
-will not show idle injection kernel threads.
-
-If the system is busy (spin test below) and has less than 25% natural
-idle time, powerclamp kernel threads will do idle injection. Forced
-idle time is accounted as normal idle in that common code path is
-taken as the idle task.
-
-In this example, 24.1% idle is shown. This helps the system admin or
-user determine the cause of slowdown, when a powerclamp driver is in action::
-
-
- Tasks: 197 total, 1 running, 196 sleeping, 0 stopped, 0 zombie
- Cpu(s): 71.2%us, 4.7%sy, 0.0%ni, 24.1%id, 0.0%wa, 0.0%hi, 0.0%si, 0.0%st
- Mem: 3943228k total, 1689632k used, 2253596k free, 74960k buffers
- Swap: 4087804k total, 0k used, 4087804k free, 945336k cached
-
- PID USER PR NI VIRT RES SHR S %CPU %MEM TIME+ COMMAND
- 3352 jacob 20 0 262m 644 428 S 286 0.0 0:17.16 spin
- 3341 root -51 0 0 0 0 D 25 0.0 0:01.62 kidle_inject/0
- 3344 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/3
- 3342 root -51 0 0 0 0 D 25 0.0 0:01.61 kidle_inject/1
- 3343 root -51 0 0 0 0 D 25 0.0 0:01.60 kidle_inject/2
- 2935 jacob 20 0 696m 125m 35m S 5 3.3 0:31.11 firefox
- 1546 root 20 0 158m 20m 6640 S 3 0.5 0:26.97 Xorg
- 2100 jacob 20 0 1223m 88m 30m S 3 2.3 0:23.68 compiz
-
-Tests have shown that by using the powerclamp driver as a cooling
-device, a PID based userspace thermal controller can manage to
-control CPU temperature effectively, when no other thermal influence
-is added. For example, a UltraBook user can compile the kernel under
-certain temperature (below most active trip points).
Q: https://patchwork.kernel.org/project/linux-pm/list/
T: git git://git.kernel.org/pub/scm/linux/kernel/git/rafael/linux-pm.git thermal
F: Documentation/ABI/testing/sysfs-class-thermal
+F: Documentation/admin-guide/thermal/
F: Documentation/devicetree/bindings/thermal/
F: Documentation/driver-api/thermal/
F: drivers/thermal/
projects / linux.git / commitdiff