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Update to CPU performance guide. (#1037)
* Changed .. code:: to .. code-block:: to match project standards. Signed-off-by: Kevin Putnam <kevin.putnam@intel.com> * Updates to power and performance for readability and consistency with project reST standards. Signed-off-by: Kevin Putnam <kevin.putnam@intel.com> * Further updates to CPU performance guide with BIOS snapshot to show what DPTF setting might look like. Signed-off-by: Kevin Putnam <kevin.putnam@intel.com> * Addressing editorial feedback. Signed-off-by: Kevin Putnam <kevin.putnam@intel.com> * Added disclaimer for Intel Turbo Boost Technology. Signed-off-by: Kevin Putnam <kevin.putnam@intel.com>
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Kevin Putnam
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@@ -13,12 +13,12 @@ Overview
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********
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Modern x86 :abbr:`CPUs (central processing units)` employ a number of features
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and technologies to balance performance, energy, and thermal efficiencies.
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to balance performance, energy, and thermal efficiency.
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By default, |CL| prioritizes maximum CPU performance with the philosophy that
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By default, |CL| prioritizes maximum CPU performance, assuming that
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the faster the program finishes execution, the faster the CPU can return to a
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low energy idle state. It is important to understand and evaluate all of these
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technologies when troubleshooting or considering changing the defaults.
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low energy idle state. It is important to understand and evaluate the impact
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of each feature when troubleshooting or considering changing the defaults.
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.. contents::
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:local:
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@@ -29,26 +29,22 @@ CPU power saving mechanisms
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C-states and P-states are both CPU power saving mechanisms that are entered
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under different operating conditions. The tradeoff is a slightly longer time
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to exit these states when the CPU is needed once again.
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to exit these states when the CPU is needed.
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.. _c-states-section:
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C-states (idle states)
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======================
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C-states are hardware sleep states that are entered when it is determined that
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the CPU is idle and not executing instructions.
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Hardware enters a C-state when the CPU is idle and not executing instructions.
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C-states decrease power utilization by reducing clock frequency,
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voltages, and features in each state. Although C-states can typically be
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limited or disabled in a system's UEFI or BIOS configuration, these settings
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are overridden when the `intel_idle driver`_ is in use.
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C-states aim to reduce power utilization by increasingly reducing clock
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frequency, voltages, and features in each state.
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To view the current ``cpuidle`` driver run this command in a terminal:
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Although C-states can typically be limited or disabled in a system's UEFI or
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BIOS configuration, these settings are overridden when the `intel_idle driver`_
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is in use.
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To view the current cpuidle driver run this command in a terminal:
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.. code:: bash
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.. code-block:: bash
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cat /sys/devices/system/cpu/cpuidle/current_driver
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@@ -58,95 +54,87 @@ or completely disabled with :command:`idle=poll`.
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.. note::
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* :command:`processor.max_cstate=0` is changed to :command:`processor.max_cstate=1`
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by the kernel to be a valid value.
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* :command:`processor.max_cstate=0` is changed to a valid value by the
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kernel: :command:`processor.max_cstate=1`.
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* :command:`intel_idle.max_cstate=0` disables the Intel Idle driver, not set
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it to C-state 0.
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* :command:`intel_idle.max_cstate=0` disables the Intel Idle driver rather
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than set it to C-state 0.
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.. _p-states-section:
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P-states (performance states)
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=============================
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P-states, also known as *Intel SpeedStep® technology* on Intel processors or
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*Cool'n'Quiet* on AMD processors, are states entered while the CPU is active and
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executing instructions.
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P-states aim to reduce power utilization by adjusting CPU clock frequency and
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voltages based on CPU demand.
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P-states can typically be limited or disabled in a system's firmware (UEFI/BIOS).
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The CPU can enter a P-state, also known as Intel SpeedStep® technology on
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Intel processors or AMD\* Cool'n'Quiet\* technology, while it is active
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and executing instructions. P-states reduce power utilization by adjusting CPU
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clock frequency and voltages based on CPU demand. P-states can typically be
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limited or disabled in a system's firmware (UEFI/BIOS).
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Turbo boost
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-----------
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`Intel® Turbo Boost Technology`_, found on some modern Intel CPUs, allows core(s) on
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a processor to temporarily operate at a higher than rated CPU clock frequency
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to accommodate demanding workloads if the CPU is under defined power and
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thermal thresholds.
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`Intel® Turbo Boost Technology`_, found on some modern Intel CPUs, allows
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cores on a processor to temporarily operate at a higher than rated CPU clock
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frequency to accommodate demanding workloads if the CPU is under defined power
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and thermal thresholds. Intel Turbo Boost Technology is an extension of
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P-states, so it can be impacted by limiting C-states or P-states.
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Turbo boost is an extension of P-states. As such, changing or limiting
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C-states or P-states impact the ability of a process to enter Turbo boost.
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Intel Turbo Boost Technology can be disabled in a system's UEFI/BIOS or in
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|CL|:
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Turbo boost can be disabled in a system's UEFI or BIOS. Turbo boost can also
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be disabled within |CL| with the command:
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.. code:: bash
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.. code-block:: bash
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echo 1 | sudo tee /sys/devices/system/cpu/intel_pstate/no_turbo
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Linux CPU clock frequency scaling
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*********************************
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The CPUFreq subsystem in Linux allows the OS to control :ref:`C-states
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<c-states-section>` and :ref:`P-states <P-states-section>`
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The ``CPUFreq`` subsystem in Linux allows the OS to control
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:ref:`C-states <c-states-section>` and :ref:`P-states <P-states-section>`
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via CPU drivers and governors that provide algorithms that define how and when
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to enter these states.
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Scaling driver
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==============
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Linux uses the `Intel P-state driver`_, :command:`intel_pstate`, for modern Intel
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processors from the Sandy Bridge generation or newer. Other processors may
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default to the :command:`acpi-cpufreq*` driver which reads values from the systems
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UEFI or BIOS.
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Linux uses the `Intel P-state driver`_, :command:`intel_pstate`, for
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modern Intel processors from the Sandy Bridge generation or newer. Other
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processors may default to the :command:`acpi-cpufreq` driver which reads
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values from the systems UEFI or BIOS.
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To view the current CPU frequency scaling driver run this command in a terminal:
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To view the current CPU frequency scaling driver, run this command in a
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terminal:
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.. code:: bash
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.. code-block:: bash
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cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_driver
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Scaling governor
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================
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|CL| sets the CPU governor to *performance* which calls for the CPU to operate
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at maximum clock frequency. In other words, P-state P0. While this may sound
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wasteful at first, it is important to remember that power utilization does not
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increase significantly simply because of a locked clock frequency without a
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workload.
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|CL| sets the CPU governor to ``performance`` which calls for the CPU to
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operate at maximum clock frequency. In other words, P-state P0. While this may
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sound wasteful at first, it is important to remember that power utilization
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does not increase significantly simply because of a locked clock frequency
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without a workload.
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To view the current CPU frequency scaling governor run this command in a terminal:
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To view the current CPU frequency scaling governor, run this command in a
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terminal:
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.. code:: bash
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.. code-block:: bash
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cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
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To change the CPU frequency scaling governor:
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Each core will report its own status. Your output should look similar to this
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example with four cores:
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#. Disable |CL| enforcement of certain power and performance settings:
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.. code-block:: console
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.. code:: bash
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sudo systemctl mask clr-power.timer
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#. Change the governor. In the example below, the governor is set to
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*performance*:
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.. code:: bash
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echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
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performance
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performance
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performance
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performance
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The list of all governors can be found in the Linux kernel documentation on
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`CPUFreq Governors`_.
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@@ -155,34 +143,49 @@ The list of all governors can be found in the Linux kernel documentation on
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The intel_pstate driver only supports *performance* and *powersave* governors.
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There are 2 ways to change the CPU frequency scaling governor:
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#. Disable |CL| enforcement of certain power and performance settings:
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.. code-block:: bash
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sudo systemctl mask clr-power.timer
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#. Change the governor value in :file:`/sys/devices`. In the example below,
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the governor is set to *performance*:
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.. code-block:: bash
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echo performance | sudo tee /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
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Thermal management
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******************
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`thermald`_ is a Linux thermal management daemon used to prevent the
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overheating of platforms. When temperature thresholds are exceeded, thermald
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forces a C-state by inserting CPU sleep cycles and adjusts available cooling
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methods. This can be especially desirable for laptops.
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`thermald`_ is a Linux thermal management daemon used to prevent platforms
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from overheating. :command:`thermald` forces a C-state by inserting CPU sleep
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cycles and adjusting any available cooling methods. This can be especially
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desirable for laptops.
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By default, thermald is disabled in |CL| and starts automatically if battery
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power is detected. thermald can be manually enabled using the systemd service
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by running the command:
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:command:`thermald` is disabled by default in |CL| and starts automatically
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if it detects battery power. Enable :command:`thermald` manually by using
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the systemd service by running the command:
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.. code:: bash
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.. code-block:: bash
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sudo systemctl enable --now thermald
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For more information, see the thermald man page:
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For more information, see the :command:`thermald` man page:
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.. code:: bash
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.. code-block:: bash
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man thermald
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`ThermalMonitor`_ is a GUI application that can visually graph and log
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temperatures from thermald. To use ThermalMonitor, add the
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temperatures from :command:`thermald`. To use ThermalMonitor, add the
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:command:`desktop-apps-extras` bundle and add your user account to the power
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group:
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.. code:: bash
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.. code-block:: bash
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sudo swupd bundle-add desktop-apps-extras
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sudo usermod -a -G power <USER>
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@@ -197,48 +200,64 @@ Enhanced thermal configuration
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===============================
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Better thermal control and performance can be achieved by providing platform
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specific configuration to thermald.
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specific configuration to :command:`thermald`.
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`Linux DPTF Extract Utility`_ is a companion tool to thermald, This tool can
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make use of :abbr:`Intel® Dynamic Platform and Thermal Framework (`Intel DPTF)`
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technology, and convert to the thermal_conf.xml configuration format used
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by thermald. It's a closed-source project, and unable to be packaged as bundle
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in Clear Linux OS, so we need to follow below steps to generate configuration.
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`Linux DPTF Extract Utility`_ is a companion tool to :command:`thermald`,
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This tool uses Intel®
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:abbr:`DPTF (Dynamic Platform and Thermal Framework)` technology and
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can convert to the :file:`thermal_conf.xml` configuration format used by
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:command:`thermald`. Closed-source projects, like this one, cannot be packaged
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as a bundle in |CL|, so you must install it manually:
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Intel DPTF requires BIOS support, it's typically used by laptops.
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The first step is to make sure your machine's BIOS has DPTF feature
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and is enabled.
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#. Make sure your machine's BIOS has DPTF feature and is enabled. It will usually be in the :guilabel:`Advanced` or :guilabel:`Advanced>Power` section of the BIOS.
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Then generate thermal configuration as below:
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.. figure:: /_figures/cpu-perf-guide/dptf_bios.png
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.. code:: bash
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.. note::
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sudo swupd bundle-add acpica-unix2 # install acpi tools
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git clone https://github.com/intel/dptfxtract.git
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cd dptfxtract
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sudo acpidump > acpi.out
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acpixtract -a acpi.out
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sudo ./dptfxtract *.dat
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Intel DPTF requires BIOS support and is typically only available on
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laptops.
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thermald configuration files will be generated and saved to
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:command:`/etc/thermal/` folder. Restart thermald service to take effect.
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#. Generate thermal configuration. :command:`thermald` configuration files
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will be generated and saved to :file:`/etc/thermal/` folder.
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.. code:: bash
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.. code-block:: bash
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sudo systemctl restart thermald.service
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sudo swupd bundle-add acpica-unix2 # install acpi tools
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git clone https://github.com/intel/dptfxtract.git
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cd dptfxtract
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sudo acpidump > acpi.out
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acpixtract -a acpi.out
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sudo ./dptfxtract *.dat
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check whether the configuration is in used.
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#. Restart :command:`thermald` service to take effect.
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.. code:: bash
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.. code-block:: bash
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sudo systemctl status thermald.service
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sudo systemctl restart thermald.service
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if the output contains below line, it means configuration already applied:
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#. Check whether the configuration is in use.
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.. code:: bash
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.. code-block:: bash
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sudo systemctl status thermald.service
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The following output means the configuration has already been applied:
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.. code-block:: console
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thermald[*]: [WARN]Using generated /etc/thermald/thermal-conf.xml.auto
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.. admonition:: Disclaimer
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Intel® Turbo Boost Technology requires a PC with a processor with Intel
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Turbo Boost Technology capability. Intel Turbo Boost Technology performance
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varies depending on hardware, software and overall system configuration.
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Check with your PC manufacturer on whether your system delivers Intel Turbo
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Boost Technology. For more information, see http://www.intel.com/technology/turboboost
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Intel SpeedStep is a trademark of Intel Corporation or its subsidiaries.
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.. _`Intel P-state driver`: https://www.kernel.org/doc/Documentation/cpu-freq/intel-pstate.txt
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