Linus Torvalds 1c3b68f0d5 Merge tag 'sched-core-2026-04-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull scheduler updates from Ingo Molnar:
 "Fair scheduling updates:
   - Skip SCHED_IDLE rq for SCHED_IDLE tasks (Christian Loehle)
   - Remove superfluous rcu_read_lock() in the wakeup path (K Prateek Nayak)
   - Simplify the entry condition for update_idle_cpu_scan() (K Prateek Nayak)
   - Simplify SIS_UTIL handling in select_idle_cpu() (K Prateek Nayak)
   - Avoid overflow in enqueue_entity() (K Prateek Nayak)
   - Update overutilized detection (Vincent Guittot)
   - Prevent negative lag increase during delayed dequeue (Vincent Guittot)
   - Clear buddies for preempt_short (Vincent Guittot)
   - Implement more complex proportional newidle balance (Peter Zijlstra)
   - Increase weight bits for avg_vruntime (Peter Zijlstra)
   - Use full weight to __calc_delta() (Peter Zijlstra)

  RT and DL scheduling updates:
   - Fix incorrect schedstats for rt and dl thread (Dengjun Su)
   - Skip group schedulable check with rt_group_sched=0 (Michal Koutný)
   - Move group schedulability check to sched_rt_global_validate()
     (Michal Koutný)
   - Add reporting of runtime left & abs deadline to sched_getattr()
     for DEADLINE tasks (Tommaso Cucinotta)

  Scheduling topology updates by K Prateek Nayak:
   - Compute sd_weight considering cpuset partitions
   - Extract "imb_numa_nr" calculation into a separate helper
   - Allocate per-CPU sched_domain_shared in s_data
   - Switch to assigning "sd->shared" from s_data
   - Remove sched_domain_shared allocation with sd_data

  Energy-aware scheduling updates:
   - Filter false overloaded_group case for EAS (Vincent Guittot)
   - PM: EM: Switch to rcu_dereference_all() in wakeup path
     (Dietmar Eggemann)

  Infrastructure updates:
   - Replace use of system_unbound_wq with system_dfl_wq (Marco Crivellari)

  Proxy scheduling updates by John Stultz:
   - Make class_schedulers avoid pushing current, and get rid of proxy_tag_curr()
   - Minimise repeated sched_proxy_exec() checking
   - Fix potentially missing balancing with Proxy Exec
   - Fix and improve task::blocked_on et al handling
   - Add assert_balance_callbacks_empty() helper
   - Add logic to zap balancing callbacks if we pick again
   - Move attach_one_task() and attach_task() helpers to sched.h
   - Handle blocked-waiter migration (and return migration)
   - Add K Prateek Nayak to scheduler reviewers for proxy execution

  Misc cleanups and fixes by John Stultz, Joseph Salisbury, Peter
  Zijlstra, K Prateek Nayak, Michal Koutný, Randy Dunlap, Shrikanth
  Hegde, Vincent Guittot, Zhan Xusheng, Xie Yuanbin and Vincent Guittot"

* tag 'sched-core-2026-04-13' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (46 commits)
  sched/eevdf: Clear buddies for preempt_short
  sched/rt: Cleanup global RT bandwidth functions
  sched/rt: Move group schedulability check to sched_rt_global_validate()
  sched/rt: Skip group schedulable check with rt_group_sched=0
  sched/fair: Avoid overflow in enqueue_entity()
  sched: Use u64 for bandwidth ratio calculations
  sched/fair: Prevent negative lag increase during delayed dequeue
  sched/fair: Use sched_energy_enabled()
  sched: Handle blocked-waiter migration (and return migration)
  sched: Move attach_one_task and attach_task helpers to sched.h
  sched: Add logic to zap balance callbacks if we pick again
  sched: Add assert_balance_callbacks_empty helper
  sched/locking: Add special p->blocked_on==PROXY_WAKING value for proxy return-migration
  sched: Fix modifying donor->blocked on without proper locking
  locking: Add task::blocked_lock to serialize blocked_on state
  sched: Fix potentially missing balancing with Proxy Exec
  sched: Minimise repeated sched_proxy_exec() checking
  sched: Make class_schedulers avoid pushing current, and get rid of proxy_tag_curr()
  MAINTAINERS: Add K Prateek Nayak to scheduler reviewers
  sched/core: Get this cpu once in ttwu_queue_cond()
  ...
2026-04-14 13:33:36 -07:00
2026-01-26 19:07:09 -08:00
2022-09-28 09:02:20 +02:00
2025-02-19 14:53:27 -07:00

Linux kernel
============

The Linux kernel is the core of any Linux operating system. It manages hardware,
system resources, and provides the fundamental services for all other software.

Quick Start
-----------

* Report a bug: See Documentation/admin-guide/reporting-issues.rst
* Get the latest kernel: https://kernel.org
* Build the kernel: See Documentation/admin-guide/quickly-build-trimmed-linux.rst
* Join the community: https://lore.kernel.org/

Essential Documentation
-----------------------

All users should be familiar with:

* Building requirements: Documentation/process/changes.rst
* Code of Conduct: Documentation/process/code-of-conduct.rst
* License: See COPYING

Documentation can be built with make htmldocs or viewed online at:
https://www.kernel.org/doc/html/latest/


Who Are You?
============

Find your role below:

* New Kernel Developer - Getting started with kernel development
* Academic Researcher - Studying kernel internals and architecture
* Security Expert - Hardening and vulnerability analysis
* Backport/Maintenance Engineer - Maintaining stable kernels
* System Administrator - Configuring and troubleshooting
* Maintainer - Leading subsystems and reviewing patches
* Hardware Vendor - Writing drivers for new hardware
* Distribution Maintainer - Packaging kernels for distros
* AI Coding Assistant - LLMs and AI-powered development tools


For Specific Users
==================

New Kernel Developer
--------------------

Welcome! Start your kernel development journey here:

* Getting Started: Documentation/process/development-process.rst
* Your First Patch: Documentation/process/submitting-patches.rst
* Coding Style: Documentation/process/coding-style.rst
* Build System: Documentation/kbuild/index.rst
* Development Tools: Documentation/dev-tools/index.rst
* Kernel Hacking Guide: Documentation/kernel-hacking/hacking.rst
* Core APIs: Documentation/core-api/index.rst

Academic Researcher
-------------------

Explore the kernel's architecture and internals:

* Researcher Guidelines: Documentation/process/researcher-guidelines.rst
* Memory Management: Documentation/mm/index.rst
* Scheduler: Documentation/scheduler/index.rst
* Networking Stack: Documentation/networking/index.rst
* Filesystems: Documentation/filesystems/index.rst
* RCU (Read-Copy Update): Documentation/RCU/index.rst
* Locking Primitives: Documentation/locking/index.rst
* Power Management: Documentation/power/index.rst

Security Expert
---------------

Security documentation and hardening guides:

* Security Documentation: Documentation/security/index.rst
* LSM Development: Documentation/security/lsm-development.rst
* Self Protection: Documentation/security/self-protection.rst
* Reporting Vulnerabilities: Documentation/process/security-bugs.rst
* CVE Procedures: Documentation/process/cve.rst
* Embargoed Hardware Issues: Documentation/process/embargoed-hardware-issues.rst
* Security Features: Documentation/userspace-api/seccomp_filter.rst

Backport/Maintenance Engineer
-----------------------------

Maintain and stabilize kernel versions:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* Backporting Guide: Documentation/process/backporting.rst
* Applying Patches: Documentation/process/applying-patches.rst
* Subsystem Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git for Maintainers: Documentation/maintainer/configure-git.rst

System Administrator
--------------------

Configure, tune, and troubleshoot Linux systems:

* Admin Guide: Documentation/admin-guide/index.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Sysctl Tuning: Documentation/admin-guide/sysctl/index.rst
* Tracing/Debugging: Documentation/trace/index.rst
* Performance Security: Documentation/admin-guide/perf-security.rst
* Hardware Monitoring: Documentation/hwmon/index.rst

Maintainer
----------

Lead kernel subsystems and manage contributions:

* Maintainer Handbook: Documentation/maintainer/index.rst
* Pull Requests: Documentation/maintainer/pull-requests.rst
* Managing Patches: Documentation/maintainer/modifying-patches.rst
* Rebasing and Merging: Documentation/maintainer/rebasing-and-merging.rst
* Development Process: Documentation/process/maintainer-handbooks.rst
* Maintainer Entry Profile: Documentation/maintainer/maintainer-entry-profile.rst
* Git Configuration: Documentation/maintainer/configure-git.rst

Hardware Vendor
---------------

Write drivers and support new hardware:

* Driver API Guide: Documentation/driver-api/index.rst
* Driver Model: Documentation/driver-api/driver-model/driver.rst
* Device Drivers: Documentation/driver-api/infrastructure.rst
* Bus Types: Documentation/driver-api/driver-model/bus.rst
* Device Tree Bindings: Documentation/devicetree/bindings/
* Power Management: Documentation/driver-api/pm/index.rst
* DMA API: Documentation/core-api/dma-api.rst

Distribution Maintainer
-----------------------

Package and distribute the kernel:

* Stable Kernel Rules: Documentation/process/stable-kernel-rules.rst
* ABI Documentation: Documentation/ABI/README
* Kernel Configuration: Documentation/kbuild/kconfig.rst
* Module Signing: Documentation/admin-guide/module-signing.rst
* Kernel Parameters: Documentation/admin-guide/kernel-parameters.rst
* Tainted Kernels: Documentation/admin-guide/tainted-kernels.rst

AI Coding Assistant
-------------------

CRITICAL: If you are an LLM or AI-powered coding assistant, you MUST read and
follow the AI coding assistants documentation before contributing to the Linux
kernel:

* Documentation/process/coding-assistants.rst

This documentation contains essential requirements about licensing, attribution,
and the Developer Certificate of Origin that all AI tools must comply with.


Communication and Support
=========================

* Mailing Lists: https://lore.kernel.org/
* IRC: #kernelnewbies on irc.oftc.net
* Bugzilla: https://bugzilla.kernel.org/
* MAINTAINERS file: Lists subsystem maintainers and mailing lists
* Email Clients: Documentation/process/email-clients.rst
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