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Chen Yu d59f4fd1d3 sched/cache: Enable cache aware scheduling for multi LLCs NUMA node
Introduce sched_cache_present to enable cache aware scheduling for
multi LLCs NUMA node Cache-aware load balancing should only be
enabled if there are more than 1 LLCs within 1 NUMA node.
sched_cache_present is introduced to indicate whether this
platform supports this topology.

Test results:
The first test platform is a 2 socket Intel Sapphire Rapids with 30
cores per socket. The DRAM interleaving is enabled in the BIOS so it
essential has one NUMA node with two last level caches. There are 60
CPUs associated with each last level cache.

The second test platform is a AMD Genoa. There are 4 Nodes and 32 CPUs
per node. Each node has 2 CCXs and each CCX has 16 CPUs.

hackbench/schbench/netperf/stream/stress-ng/chacha20 were launched
on these two platforms.

[TL;DR]
Sappire Rapids:
hackbench shows significant improvement when the number of
different active threads is below the capacity of a LLC.
schbench shows limitted wakeup latency improvement.
ChaCha20-xiangshan(risc-v simulator) shows good throughput
improvement. No obvious difference was observed in
netperf/stream/stress-ng in Hmean.

Genoa:
Significant improvement is observed in hackbench when
the active number of threads is lower than the number
of CPUs within 1 LLC. On v2, Aaron reported improvement
of hackbench/redis when system is underloaded.
ChaCha20-xiangshan shows huge throughput improvement.
Phoronix has tested v1 and shows good improvements in 30+
cases[3]. No obvious difference was observed in
netperf/stream/stress-ng in Hmean.

Detail:
Due to length constraints, data without much difference with
baseline is not presented.

Sapphire Rapids:
[hackbench pipe]
================
case                    load            baseline(std%)  compare%( std%)
threads-pipe-10         1-groups         1.00 (  1.22)  +26.09 (  1.10)
threads-pipe-10         2-groups         1.00 (  4.90)  +22.88 (  0.18)
threads-pipe-10         4-groups         1.00 (  2.07)   +9.00 (  3.49)
threads-pipe-10         8-groups         1.00 (  8.13)   +3.45 (  3.62)
threads-pipe-16         1-groups         1.00 (  2.11)  +26.30 (  0.08)
threads-pipe-16         2-groups         1.00 ( 15.13)   -1.77 ( 11.89)
threads-pipe-16         4-groups         1.00 (  4.37)   +0.58 (  7.99)
threads-pipe-16         8-groups         1.00 (  2.88)   +2.71 (  3.50)
threads-pipe-2          1-groups         1.00 (  9.40)  +22.07 (  0.71)
threads-pipe-2          2-groups         1.00 (  9.99)  +18.01 (  0.95)
threads-pipe-2          4-groups         1.00 (  3.98)  +24.66 (  0.96)
threads-pipe-2          8-groups         1.00 (  7.00)  +21.83 (  0.23)
threads-pipe-20         1-groups         1.00 (  1.03)  +28.84 (  0.21)
threads-pipe-20         2-groups         1.00 (  4.42)  +31.90 (  3.15)
threads-pipe-20         4-groups         1.00 (  9.97)   +4.56 (  1.69)
threads-pipe-20         8-groups         1.00 (  1.87)   +1.25 (  0.74)
threads-pipe-4          1-groups         1.00 (  4.48)  +25.67 (  0.78)
threads-pipe-4          2-groups         1.00 (  9.14)   +4.91 (  2.08)
threads-pipe-4          4-groups         1.00 (  7.68)  +19.36 (  1.53)
threads-pipe-4          8-groups         1.00 ( 10.79)   +7.20 ( 12.20)
threads-pipe-8          1-groups         1.00 (  4.69)  +21.93 (  0.03)
threads-pipe-8          2-groups         1.00 (  1.16)  +25.29 (  0.65)
threads-pipe-8          4-groups         1.00 (  2.23)   -1.27 (  3.62)
threads-pipe-8          8-groups         1.00 (  4.65)   -3.08 (  2.75)

Note: The default number of fd in hackbench is changed from 20 to various
values to ensure that threads fit within a single LLC, especially on AMD
systems. Take "threads-pipe-8, 2-groups" for example, the number of fd
is 8, and 2 groups are created.

[schbench]
The 99th percentile wakeup latency shows some improvements when the
system is underload, while it does not bring much difference with
the increasing of system utilization.

99th Wakeup Latencies	Base (mean std)      Compare (mean std)   Change
=========================================================================
thread=2                 9.00(0.00)           9.00(1.73)           0.00%
thread=4                 7.33(0.58)           6.33(0.58)           +13.64%
thread=8                 9.00(0.00)           7.67(1.15)           +14.78%
thread=16                8.67(0.58)           8.67(1.53)           0.00%
thread=32                9.00(0.00)           7.00(0.00)           +22.22%
thread=64                9.33(0.58)           9.67(0.58)           -3.64%
thread=128              12.00(0.00)          12.00(0.00)           0.00%

[chacha20 on simulated risc-v]
baseline:
Host time spent: 67861ms
cache aware scheduling enabled:
Host time spent: 54441ms

Time reduced by 24%

Genoa:
[hackbench pipe]
The default number of fd is 20, which exceed the number of CPUs
in a LLC. So the fd is adjusted to 2, 4, 6, 8, 20 respectively.
Exclude the result with large run-to-run variance, 10% ~ 50%
improvement is observed when the system is underloaded:

[hackbench pipe]
================
case                    load            baseline(std%)  compare%( std%)
threads-pipe-2          1-groups         1.00 (  2.89)  +47.33 (  1.20)
threads-pipe-2          2-groups         1.00 (  3.88)  +39.82 (  0.61)
threads-pipe-2          4-groups         1.00 (  8.76)   +5.57 ( 13.10)
threads-pipe-20         1-groups         1.00 (  4.61)  +11.72 (  1.06)
threads-pipe-20         2-groups         1.00 (  6.18)  +14.55 (  1.47)
threads-pipe-20         4-groups         1.00 (  2.99)  +10.16 (  4.49)
threads-pipe-4          1-groups         1.00 (  4.23)  +43.70 (  2.14)
threads-pipe-4          2-groups         1.00 (  3.68)   +8.45 (  4.04)
threads-pipe-4          4-groups         1.00 ( 17.72)   +2.42 (  1.14)
threads-pipe-6          1-groups         1.00 (  3.10)   +7.74 (  3.83)
threads-pipe-6          2-groups         1.00 (  3.42)  +14.26 (  4.53)
threads-pipe-6          4-groups         1.00 ( 10.34)  +10.94 (  7.12)
threads-pipe-8          1-groups         1.00 (  4.21)   +9.06 (  4.43)
threads-pipe-8          2-groups         1.00 (  1.88)   +3.74 (  0.58)
threads-pipe-8          4-groups         1.00 (  2.78)  +23.96 (  1.18)

[chacha20 on simulated risc-v]
Host time spent: 54762ms
Host time spent: 28295ms

Time reduced by 48%

Suggested-by: Libo Chen <libchen@purestorage.com>
Suggested-by: Adam Li <adamli@os.amperecomputing.com>
Signed-off-by: Chen Yu <yu.c.chen@intel.com>
Co-developed-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Tim Chen <tim.c.chen@linux.intel.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://patch.msgid.link/71972e12ab4f08aff422b31e34df09bdbd94de84.1775065312.git.tim.c.chen@linux.intel.com
History 2026-04-09 15:49:51 +02:00
arch x86/topology: Add paramter to split LLC 2026-04-09 15:49:46 +02:00
block block-7.0-20260305 2026-03-06 08:36:18 -08:00
certs Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
crypto crypto: testmgr - Fix stale references to aes-generic 2026-03-03 11:57:15 -08:00
Documentation x86/topology: Add paramter to split LLC 2026-04-09 15:49:46 +02:00
drivers phy fixes for 7.0 2026-03-29 12:48:52 -07:00
fs vfs-7.0-rc6.fixes 2026-03-29 15:24:28 -07:00
include sched/cache: Introduce per CPU's tasks LLC preference counter 2026-04-09 15:49:49 +02:00
init sched/cache: Assign preferred LLC ID to processes 2026-04-09 15:49:49 +02:00
io_uring io_uring-7.0-20260327 2026-03-27 15:35:38 -07:00
ipc Convert 'alloc_obj' family to use the new default GFP_KERNEL argument 2026-02-21 17:09:51 -08:00
kernel sched/cache: Enable cache aware scheduling for multi LLCs NUMA node 2026-04-09 15:49:51 +02:00
lib bug: avoid format attribute warning for clang as well 2026-03-27 20:48:38 -07:00
LICENSES LICENSES: Add modern form of the LGPL-2.1 tags to the usage guide section 2025-10-22 07:58:19 +02:00
mm Miscellaneous futex fixes: 2026-03-29 09:59:46 -07:00
net netfilter pull request 26-03-26 2026-03-26 15:38:14 +01:00
rust rust: regulator: do not assume that regulator_get() returns non-null 2026-03-24 13:08:21 +00:00
samples Landlock fix for v7.0-rc6 2026-03-26 12:03:37 -07:00
scripts hardening fixes for v7.0-rc6 2026-03-25 14:47:18 -07:00
security Landlock fix for v7.0-rc6 2026-03-26 12:03:37 -07:00
sound Revert "ALSA: hda/intel: Add MSI X870E Tomahawk to denylist" 2026-03-27 10:54:04 +01:00
tools vfs-7.0-rc6.fixes 2026-03-29 15:24:28 -07:00
usr kbuild: uapi: drop dependency on CC_CAN_LINK 2026-01-16 15:02:11 -07:00
virt KVM generic changes for 7.0 2026-03-11 18:01:55 +01:00
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: clean Rust 1.88.0's warning about clippy::disallowed_macros configuration 2025-05-07 00:11:47 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore MAINTAINERS: remove Alyssa Rosenzweig 2025-09-18 21:17:31 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: kbuild: add proc macro library support 2025-11-24 17:15:36 +01:00
.mailmap MAINTAINERS, mailmap: update email address for Harry Yoo 2026-03-27 20:48:37 -07:00
.pylintrc docs: Move the python libraries to tools/lib/python 2025-11-18 09:22:40 -07:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: remove Thomas Falcon from IBM ibmvnic 2026-03-05 07:35:45 -08:00
Kbuild sched: Make migrate_{en,dis}able() inline 2025-09-25 09:57:16 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS Merge branch 'sched/urgent' into sched/core, to resolve conflicts 2026-04-02 15:04:09 +02:00
Makefile Linux 7.0-rc6 2026-03-29 15:40:00 -07:00
README docs: add AI Coding Assistants documentation 2026-01-06 14:55:06 -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