linux-kernel - [PATCH v2 00/10] PM: EM: Add netlink support for the energy model.

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Message-ID: <20250613094428.267791-1-changwoo@igalia.com>
Date: Fri, 13 Jun 2025 18:44:18 +0900
From: Changwoo Min <changwoo@...lia.com>
To: lukasz.luba@....com,
	rafael@...nel.org,
	len.brown@...el.com,
	pavel@...nel.org
Cc: christian.loehle@....com,
	tj@...nel.org,
	kernel-dev@...lia.com,
	linux-pm@...r.kernel.org,
	sched-ext@...ts.linux.dev,
	linux-kernel@...r.kernel.org,
	Changwoo Min <changwoo@...lia.com>,
	"Rafael J. Wysocki" <rafael.j.wysocki@...el.com>
Subject: [PATCH v2 00/10] PM: EM: Add netlink support for the energy model.

There is a need to access the energy model from the userspace. One such
example is the sched_ext schedulers [1]. The userspace part of the
sched_ext schedules could feed the (post-processed) energy-model
information to the BPF part of the scheduler.

Currently, debugfs is the only way to read the energy model from userspace;
however, it lacks proper notification mechanisms when a performance domain
and its associated energy model change.

This patch set introduces a generic netlink for the energy model, as
discussed in [2]. It allows a userspace program to read the performance
domain and its energy model. It notifies the userspace program when a
performance domain is created or deleted or its energy model is updated
through a multicast interface.

Specifically, it supports two commands:
  - EM_CMD_GET_PDS: Get the list of information for all performance
    domains.
  - EM_CMD_GET_PD_TABLE: Get the energy model table of a performance
    domain.

Also, it supports three notification events:
  - EM_CMD_PD_CREATED: When a performance domain is created.
  - EM_CMD_PD_DELETED: When a performance domain is deleted.
  - EM_CMD_PD_UPDATED: When the energy model table of a performance domain
    is updated.

This can be tested using the tool, tools/net/ynl/pyynl/cli.py, for example,
with the following commands:

  $> tools/net/ynl/pyynl/cli.py \
     --spec Documentation/netlink/specs/em.yaml \
     --do get-pds
  $> tools/net/ynl/pyynl/cli.py \
     --spec Documentation/netlink/specs/em.yaml \
     --do get-pd-table --json '{"pd-id": 0}'
  $> tools/net/ynl/pyynl/cli.py \
     --spec Documentation/netlink/specs/em.yaml \
     --subscribe event  --sleep 10

[1] https://lwn.net/Articles/922405/
[2] https://lore.kernel.org/lkml/a82423bc-8c38-4d57-93da-c4f20011cc92@arm.com/

ChangeLog v1 -> v2:
  - Use YNL to generate boilerplate code. Overhaul the naming conventions
    (command, event, notification, attribute) to follow the typical
    conventions of other YNL-based netlink implementations.
  - Calculate the exact message size instead of using NLMSG_GOODSIZE
    when allocating a message (genlmsg_new). This avoids the reallocation
    of a message.
  - Remove an unnecessary function, em_netlink_exit(), and initialize the
    netlink (em_netlink_init) at em_netlink.c without touching energy_model.c.

CC: Lukasz Luba <lukasz.luba@....com>
CC: Rafael J. Wysocki <rafael.j.wysocki@...el.com>
CC: Tejun Heo <tj@...nel.org>
Signed-off-by: Changwoo Min <changwoo@...lia.com>

Changwoo Min (10):
  PM: EM: Add em.yaml and autogen files.
  PM: EM: Add a skeleton code for netlink notification.
  PM: EM: Assign a unique ID when creating a performance domain.
  PM: EM: Expose the ID of a performance domain via debugfs.
  PM: EM: Add an iterator and accessor for the performance domain.
  PM: EM: Implement em_nl_get_pds_doit().
  PM: EM: Implement em_nl_get_pd_table_doit().
  PM: EM: Implement em_notify_pd_deleted().
  PM: EM: Implement em_notify_pd_created/updated().
  PM: EM: Notify an event when the performance domain changes.

 Documentation/netlink/specs/em.yaml | 113 ++++++++++
 MAINTAINERS                         |   3 +
 include/linux/energy_model.h        |  19 ++
 include/uapi/linux/energy_model.h   |  62 ++++++
 kernel/power/Makefile               |   5 +-
 kernel/power/em_netlink.c           | 311 ++++++++++++++++++++++++++++
 kernel/power/em_netlink.h           |  34 +++
 kernel/power/em_netlink_autogen.c   |  48 +++++
 kernel/power/em_netlink_autogen.h   |  23 ++
 kernel/power/energy_model.c         |  83 +++++++-
 10 files changed, 699 insertions(+), 2 deletions(-)
 create mode 100644 Documentation/netlink/specs/em.yaml
 create mode 100644 include/uapi/linux/energy_model.h
 create mode 100644 kernel/power/em_netlink.c
 create mode 100644 kernel/power/em_netlink.h
 create mode 100644 kernel/power/em_netlink_autogen.c
 create mode 100644 kernel/power/em_netlink_autogen.h

-- 
2.49.0