geopmdpy 3.0.1

GEOPM - Global Extensible Open Power Manager Daemon

Features

Linux Integration

The Linux Systemd Service is integrated with a DBus interface, enabling user-level access to hardware features on heterogeneous systems.

Hardware Telemetry

Use a vendor-agnostic interface to read telemetry from hardware components on heterogeneous systems.

Hardware Configuration

User-friendly vendor-agnostic interface for configuring hardware component device settings on heterogeneous systems.

Quality of Service

The GEOPM Service reverts any changes made to hardware configurations once the client’s Linux process session concludes.

Security

Linux system administrators have complete control over managing fine-grained access permissions for capabilities exposed by the GEOPM Service.

Performance

A DBus interface can be utilized for the creation of a batch server. The server provides a low-latency interface with a single permissions validation when the server is created.

Extensibility

GEOPM Service supports extensibility for heterogeneous environments through the C++ plugin infrastructure called IOGroups.

Overview

The GEOPM Service provides an interface at the user level, allowing users to read telemetry and configure heterogeneous hardware platforms. Linux system administrators can manage the permissions for user access to telemetry and configuration at very detailed level.

The GEOPM Service DBus interface is how clients interact with the service. Access to the DBus interfaces can be gained from the command line or programmatically with library interfaces for C, C++, and Python.

The service supports multiple simultaneous client sessions for making measurements, however only clients from within a single Linux process session are given write permission to configure hardware control values at any one time. Upon termination of a client’s process session leader, the GEOPM Service restores all hardware settings to their original state before the first client’s write request.

For more information about the Linux session leader process, please consult the setsid(2) manual.

• Overview slides

Architecture

The architectural diagram shows the relationship between IOGroups and the GEOPM Service. IOGroups are the C++ classes that abstract hardware interfaces. IOGroups provide a plugin mechanism to extend GEOPM’s functionality.

The PlatformIO interface is a container for all IOGroups and is the main interface for users who interact with the hardware through the GEOPM Service. The PlatformIO interface can be accessed through language bindings with Python, C, and C++ as well as command line tools such as geopmread and geopmwrite. The GEOPM DBus interface, io.github.geopm, provides a secure gateway to privileged PlatformIO features. The geopmaccess command line tool is used by the administrator to enable user level access to any subset of the privileged PlatformIO features.

Status

The GEOPM systemd service introduced in version 2.0 is fully tested and is now ready for production.

Signals and Controls

Each signal and control in GEOPM has a unique name and a hardware domain. The signals and controls available on your system can be discovered with the geopmaccess command line tool. The description includes all the necessary information for end users and system administrators to understand what is enabled when granting access to a signal or control.

Access Management

System administrators configure the access to signals and controls through the GEOPM Service. The administrator maintains an access list that applies to all users of the system. Special Unix groups can have enhanced access. The default lists are stored in:

/etc/geopm/0.DEFAULT_ACCESS/allowed_signals
/etc/geopm/0.DEFAULT_ACCESS/allowed_controls

Each Unix group name <GROUP> that has extended permissions can maintain one or both of the files

/etc/geopm/<GROUP>/allowed_signals
/etc/geopm/<GROUP>/allowed_controls

Note

Before GEOPM 3.0, service configuration files were stored in /etc/geopm-service. Since version 3.0, they are stored in /etc/geopm. Version 3.0 ignores the old file location if the new location exists. If the service uses a configuration from the old location, then a deprecation warning is emitted.

Any missing files are inferred to be empty lists, including the default access files. A signal or control will not be available to non-root users through the GEOPM Service until a system administrator enables access through these allow lists. It is recommended that all manipulation of these files should be done through the GEOPM Service with the geopmaccess command line tool.

All control settings can be read by requesting the signal with the same name. Whenever a control name is added to the access list for writing, the administrator implicitly grants read access to the control setting as well.

Opening a Session

Each time a client process opens a session with the GEOPM Service, a PlatformIO object is created with libgeopmd. This session starts in read-only mode. Calls to the DBus APIs that modify control values convert the session into write mode. The session retains write access until it ends. Calls into the DBus APIs that modify control values:

io.github.geopm.PlatformWriteControl
io.github.geopm.PlatformPushControl

convert the session into write mode. Only one write mode session is allowed at any time. The request will fail if a client attempts to begin a write session while another client has one open.

When a session is converted to write mode, all controls that the service is configured to support are recorded to a save directory in:

/run/geopm/SAVE_FILES

When a write mode session ends, all of these saved controls are restored to the value they had when the session was converted, regardless of whether or not they were adjusted during the session through the service.

In addition to saving the state of controls, the GEOPM Service will also lock access to controls for any other client until the controlling session ends. When the controlling session ends the saved state is used to restore the values for all controls supported by the GEOPM Service to the values they had prior to enabling the client to modify a control. The controlling session may end by an explicit D-Bus call by the client, or when the process that initiated the client session ends. The GEOPM Service will poll procfs for the process ID.

Batch Server

The GEOPM Service provides the implementation for the ServiceIOGroup which accesses this implementation through the DBus interface. When a user program calls read_signal() or write_control() on a PlatformIO object provided by libgeopmd and the only IOGroup that provides the signal or control requested is the ServiceIOGroup, then each request goes through the slow DBus interface. When a client process uses the ServiceIOGroup for batch operations a separate batch server process is created through the DBus interface. The implementations for push_signal() and push_control() are used to configure the stack of signals and controls that will be enabled by the batch server. This batch server interacts more directly with the client process to provide low latency support for the read_batch() and write_batch() interfaces of the ServiceIOGroup.

The batch server is configured to allow access to exactly the signals and controls that were pushed onto the stack for the ServiceIOGroup prior to the first read_batch() or write_batch() call. Through the DBus implementation, the GEOPM Service verifies that the client user has appropriate permissions for the requested signals and controls. When the first call to read_batch() or write_batch() is made to user’s PlatformIO object, the geopmd process forks the batch server process and no more updates can be made to the configured requests. The batch server uses inter-process shared memory and FIFO special files to enable fast access to the configured stack of GEOPM signals and controls.

To implement the read_batch() method, the ServiceIOGroup writes a character to a FIFO to notify the batch server that it would like the configured GEOPM signals to be updated in shared memory. The client process then waits on a FIFO for a message from the server that the request is ready. The batch server proceeds to read all GEOPM signals that are supported by the client’s ServiceIOGroup using the batch server’s instance of the PlatformIO object. GEOPM signals are copied into the shared memory buffer and when the buffer is ready, a character is written into the FIFO that the client process is waiting on.

To implement the write_batch() method, the client process’s ServiceIOGroup prepares the shared memory buffer with all control settings that the batch server is supporting. The client then writes a character into a FIFO to notify the batch server that it would like the configured GEOPM controls to be written. The client process then waits on a FIFO for a message from the server that the controls have been written. The batch server proceeds to read the clients settings from the shared memory buffer and writes the values through the server process’s PlatformIO instance. When the write has completed, a character is written into the FIFO that the client process is waiting on.