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b78b0b6582
Runtime constify the read-only after init data __futex_shift(shift_32),
__futex_mask(mask_32), and __futex_queues(ptr) used in __futex_hash()
hot path to avoid referencing global variable.
This also allows __futex_queues to be allocated dynamically to
"nr_node_ids" slots instead of reserving config dependent MAX_NUMNODES
(1 << CONFIG_NODES_SHIFT) worth of slots upfront.
Runtime constants are initialized before their first access and
runtime_const_init() provides necessary barrier to ensure subsequent
accesses are not reordered against their initialization.
No functional changes intended.
perf bench futex on a 3rd Gen EPYC (2 x 64C/128T):
+----------------+-----------+-----------+-----------+--------------+
| Benchmark | Kernel 1 | Kernel 2 | Unit | % Improvement|
| | (avg/5) | (avg/5) | | (K2 vs K1) |
+----------------+-----------+-----------+-----------+--------------+
| Wake-parallel | 0.01614 | 0.00456 | ms | +71.75% |
| Requeue | 0.26394 | 0.24644 | ms | +6.63% |
| Lock-pi | 34.0 | 57.2 | ops/sec | +68.24% |
+----------------+-----------+-----------+-----------+--------------+
Performance testing on a 144-thread Intel(R) Xeon(R) CPU E7-8890 v3 (4 NUMA nodes):
+-------------------------------------------------------------+
| perf bench futex hash -b 0 |
+----------------------+------------+------------+------------+
| Configuration | As-is | Patched | Delta |
+----------------------+------------+------------+------------+
| 1 thread, 1 futex | 6,449,632 | 6,532,004 | +1.28% |
| 144 threads, 1024 fx | 2,111,486 | 2,139,685 | +1.34% |
+----------------------+------------+------------+------------+i
[ prateek: Dynamically allocate __futex_queues, mark the global data
__ro_after_init since they are constified after futex_init(). ]
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> # MAX_NUMNODES bloat
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Tested-by: Charlie Jenkins <thecharlesjenkins@gmail.com>
Link: https://patch.msgid.link/20260227161841.GH606826@noisy.programming.kicks-ass.net
Link: https://patch.msgid.link/20260728052540.4728-9-kprateek.nayak@amd.com
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| README | ||
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. 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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. 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