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Dragos Tatulea 2dfaa02387 net/mlx5e: XDP, Remove stride size limitation
Currently XDP mode always uses PAGE_SIZE strides. This limitation
existed because page fragment counting was not implemented when XDP was
added. Furthermore, due to this limitation there were other issues as
well on system with larger pages (e.g. 64K):

- XDP for Striding RQ was effectively disabled on such systems.

- Legacy RQ allows the configuration but uses a fixed scheme of one XDP
  buffer per page which is inefficient.

As fragment counting was added during the driver conversion to
page_pool and the support for XDP multi-buffer, it is now possible
to remove this stride size limitation. This patch does just that.

Now it is possible to use XDP on systems with higher page sizes (e.g.
64K):

- For Striding RQ, loading the program is no longer blocked.
  Although a 64K page can fit any packet, MTUs that result in
  stride > 8K will still make the RQ in non-linear mode. That's
  because the HW doesn't support a higher than 8K stride.

- For Legacy RQ, the stride size was PAGE_SIZE which was very
  inefficient. Now the stride size will be calculated relative to MTU.
  Legacy RQ will always be in linear mode for larger system pages.

  This can be observed with an XDP_DROP test [1] when running
  in Legacy RQ mode on a ARM Neoverse-N1 system with a 64K
  page size:
  +-----------------------------------------------+
  | MTU  | baseline   | this change | improvement |
  |------+------------+-------------+-------------|
  | 1500 | 15.55 Mpps | 18.99 Mpps  | 22.0 %      |
  | 9000 | 15.53 Mpps | 18.24 Mpps  | 17.5 %      |
  +-----------------------------------------------+

There are performance benefits for Striding RQ mode as well:

- Striding RQ non-linear mode now uses 256B strides, just like
  non-XDP mode.

- Striding RQ linear mode can now fit a number of XDP buffers per page
  that is relative to the MTU size. That means that on 4K page systems
  and a small enough MTU, 2 XDP buffers can fit in one page.

The above benefits for Striding RQ can be observed with an
XDP_DROP test [1] when running on a 4K page x86_64 system
(Intel Xeon Platinum 8580):
  +-----------------------------------------------+
  | MTU  | baseline   | this change | improvement |
  |------+------------+-------------+-------------|
  | 1000 | 28.36 Mpps | 33.98 Mpps  | 19.82 %     |
  | 9000 | 20.76 Mpps | 26.30 Mpps  | 26.70 %     |
  +-----------------------------------------------+

[1] Test description:
- xdp-bench with XDP_DROP
- RX: single queue
- TX: sends 64B packets to saturate CPU on RX side

Signed-off-by: Dragos Tatulea <dtatulea@nvidia.com>
Reviewed-by: Carolina Jubran <cjubran@nvidia.com>
Signed-off-by: Tariq Toukan <tariqt@nvidia.com>
Link: https://patch.msgid.link/20260403090927.139042-4-tariqt@nvidia.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
History 2026-04-07 13:34:04 +02:00
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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