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A system often runs multiple workloads especially in multi-tenant server environments where a system is split into partitions servicing separate more-or-less independent workloads each requiring an application-specific scheduler. To support such and other use cases, sched_ext is in the process of growing multiple scheduler support. When partitioning a system in terms of CPUs for such use cases, an oft-taken approach is hard partitioning the system using cpuset. While it would be possible to tie sched_ext multiple scheduler support to cpuset partitions, such an approach would have fundamental limitations stemming from the lack of dynamism and flexibility. Users often don't care which specific CPUs are assigned to which workload and want to take advantage of optimizations which are enabled by running workloads on a larger machine - e.g. opportunistic over-commit, improving latency critical workload characteristics while maintaining bandwidth fairness, employing control mechanisms based on different criteria than on-CPU time for e.g. flexible memory bandwidth isolation, packing similar parts from different workloads on same L3s to improve cache efficiency, and so on. As this sort of dynamic behaviors are impossible or difficult to implement with hard partitioning, sched_ext is implementing cgroup sub-sched support where schedulers can be attached to the cgroup hierarchy and a parent scheduler is responsible for controlling the CPUs that each child can use at any given moment. This makes CPU distribution dynamically controlled by BPF allowing high flexibility. This patch adds the skeletal sched_ext cgroup sub-sched support: - sched_ext_ops.sub_cgroup_id and .sub_attach/detach() are added. Non-zero sub_cgroup_id indicates that the scheduler is to be attached to the identified cgroup. A sub-sched is attached to the cgroup iff the nearest ancestor scheduler implements .sub_attach() and grants the attachment. Max nesting depth is limited by SCX_SUB_MAX_DEPTH. - When a scheduler exits, all its descendant schedulers are exited together. Also, cgroup.scx_sched added which points to the effective scheduler instance for the cgroup. This is updated on scheduler init/exit and inherited on cgroup online. When a cgroup is offlined, the attached scheduler is automatically exited. - Sub-sched support is gated on CONFIG_EXT_SUB_SCHED which is automatically enabled if both SCX and cgroups are enabled. Sub-sched support is not tied to the CPU controller but rather the cgroup hierarchy itself. This is intentional as the support for cpu.weight and cpu.max based resource control is orthogonal to sub-sched support. Note that CONFIG_CGROUPS around cgroup subtree iteration support for scx_task_iter is replaced with CONFIG_EXT_SUB_SCHED for consistency. - This allows loading sub-scheds and most framework operations such as propagating disable down the hierarchy work. However, sub-scheds are not operational yet and all tasks stay with the root sched. This will serve as the basis for building up full sub-sched support. - DSQs point to the scx_sched they belong to. - scx_qmap is updated to allow attachment of sub-scheds and also serving as sub-scheds. - scx_is_descendant() is added but not yet used in this patch. It is used by later changes in the series and placed here as this is where the function belongs. Signed-off-by: Tejun Heo <tj@kernel.org> Reviewed-by: Andrea Righi <arighi@nvidia.com> |
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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