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Shradha Gupta 5316394b17 net: mana: Optimize irq affinity for low vcpu configs
Before the commit 7553911210 ("net: mana: Allocate MSI-X vectors
dynamically"), all the MANA IRQs were assigned statically and together
during early driver load.

After this commit, the IRQ allocation for MANA was done in two phases.
HWC IRQ allocated earlier and then, queue IRQs dynamically added at a
later point. By this time, the IRQ weights on vCPUs can become imbalanced
and if IRQ count is greater than the vCPU count the topology aware IRQ
distribution logic in MANA can cause multiple MANA IRQs to land on the
same vCPUs, while other sibling vCPUs have none (case 1).

On SMP enabled, low-vCPU systems, this becomes a bigger problem as the
softIRQ handling overhead of two IRQs on the same vCPUs becomes much more
than their overheads if they were spread across sibling vCPUs.

In such cases when many parallel TCP connections are tested, the
throughput drops significantly.

Fix the affinity assignment logic, in cases where the IRQ count is greater
than the vCPU count and when IRQs are added dynamically, by utilizing all
the vCPUs irrespective of their NUMA/core bindings (case 2).

The results of setting the affinity and hint to NULL were also studied,
and we observed that, with this logic if there are pre-existing IRQs
allocated on the VM (apart from MANA), during MANA IRQs allocation, it
leads to clustering of the MANA queue IRQs again (case 3).

=======================================================
Case 1: without this patch
=======================================================
4 vcpu(2 cores), 5 MANA IRQs (1 HWC + 4 Queue)

	TYPE		effective vCPU aff
=======================================================
IRQ0:	HWC		0
IRQ1:	mana_q1		0
IRQ2:	mana_q2		2
IRQ3:	mana_q3		0
IRQ4:	mana_q4		3

%soft on each vCPU(mpstat -P ALL 1) on receiver
vCPU		0	1	2	3
=======================================================
pass 1:		38.85	0.03	24.89	24.65
pass 2:		39.15	0.03	24.57	25.28
pass 3:		40.36	0.03	23.20	23.17

=======================================================
Case 2: with this patch
=======================================================
4 vcpu(2 cores), 5 MANA IRQs (1 HWC + 4 Queue)

        TYPE            effective vCPU aff
=======================================================
IRQ0:   HWC             0
IRQ1:   mana_q1         0
IRQ2:   mana_q2         1
IRQ3:   mana_q3         2
IRQ4:   mana_q4         3

%soft on each vCPU(mpstat -P ALL 1) on receiver
vCPU            0       1       2       3
=======================================================
pass 1:         15.42	15.85	14.99	14.51
pass 2:         15.53	15.94	15.81	15.93
pass 3:         16.41	16.35	16.40	16.36

=======================================================
Case 3: with affinity set to NULL
=======================================================
4 vCPU(2 cores), 5 MANA IRQs (1 HWC + 4 Queue)

	TYPE		effective vCPU aff
=======================================================
IRQ0:	HWC			0
IRQ1:	mana_q1			2
IRQ2:	mana_q2			3
IRQ3:	mana_q3			2
IRQ4:	mana_q4			3

=======================================================
Throughput Impact(in Gbps, same env)
=======================================================
TCP conn	with patch	w/o patch	aff NULL
20480		15.65		7.73		5.25
10240		15.63		8.93		5.77
8192		15.64		9.69		7.16
6144		15.64		13.16		9.33
4096		15.69		15.75		13.50
2048		15.69		15.83		13.61
1024		15.71		15.28		13.60

Fixes: 7553911210 ("net: mana: Allocate MSI-X vectors dynamically")
Cc: stable@vger.kernel.org
Co-developed-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Signed-off-by: Erni Sri Satya Vennela <ernis@linux.microsoft.com>
Signed-off-by: Shradha Gupta <shradhagupta@linux.microsoft.com>
Reviewed-by: Haiyang Zhang <haiyangz@microsoft.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Reviewed-by: Yury Norov <ynorov@nvidia.com>
Link: https://patch.msgid.link/20260624072138.1632849-1-shradhagupta@linux.microsoft.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
2026-06-25 09:10:35 -07:00
arch Networking changes for 7.2. 2026-06-17 08:17:00 +01:00
block - small cleanups in dm-vdo, dm-raid, dm-cache, dm-zoned-metadata 2026-06-16 13:20:54 +05:30
certs Clang build fixes for 7.1 2026-04-24 09:29:51 -07:00
crypto Networking changes for 7.2. 2026-06-17 08:17:00 +01:00
Documentation net: ethernet: qualcomm: ppe: Demote from supported and fix maintainer addresses 2026-06-25 08:46:29 -07:00
drivers net: mana: Optimize irq affinity for low vcpu configs 2026-06-25 09:10:35 -07:00
fs Networking changes for 7.2. 2026-06-17 08:17:00 +01:00
include netfilter pull request 26-06-23 2026-06-24 19:56:59 -07:00
init Bootconfig updates for v7.2 2026-06-16 17:29:24 +05:30
io_uring Networking changes for 7.2. 2026-06-17 08:17:00 +01:00
ipc kernel-7.2-rc1.misc 2026-06-15 03:05:50 +05:30
kernel tracing latency updates for 7.2: 2026-06-16 17:38:19 +05:30
lib Bootconfig updates for v7.2 2026-06-16 17:29:24 +05:30
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 for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
net tipc: avoid busy looping in tipc_exit_net() 2026-06-25 08:53:00 -07:00
rust for-7.2/block-20260615 2026-06-16 13:02:47 +05:30
samples Driver core changes for 7.2-rc1 2026-06-15 12:41:17 +05:30
scripts linux_kselftest-kunit-7.2-rc1 2026-06-16 16:33:57 +05:30
security Networking changes for 7.2. 2026-06-17 08:17:00 +01:00
sound gpio updates for v7.2-rc1 2026-06-16 07:30:52 +05:30
tools selftests: tls: size splice_short pipe by page size 2026-06-25 09:01:58 -07:00
usr kbuild: uapi: also test UAPI headers against C++ compilers 2026-03-25 13:24:42 +01:00
virt vfs-7.2-rc1.misc 2026-06-15 03:59:45 +05:30
.clang-format Devicetree updates for v7.0: 2026-02-11 18:27:08 -08:00
.clippy.toml rust: bump Clippy's MSRV and clean incompatible_msrv allows 2026-04-07 09:51:39 +02:00
.cocciconfig
.editorconfig editorconfig: add rst extension 2026-01-26 19:07:09 -08:00
.get_maintainer.ignore .get_maintainer.ignore: add myself 2026-04-02 16:48:25 +02:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore Rust changes for v7.2 2026-06-15 09:25:48 +05:30
.mailmap net: ethernet: qualcomm: ppe: Demote from supported and fix maintainer addresses 2026-06-25 08:46:29 -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
CREDITS fbdev fixes & cleanups for 7.2-rc1: 2026-06-16 08:28:41 +05:30
Kbuild checksyscalls: move instance functionality into generic code 2026-04-05 09:21:32 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS net: ethernet: qualcomm: ppe: Demote from supported and fix maintainer addresses 2026-06-25 08:46:29 -07:00
Makefile slab changes for 7.2 2026-06-16 08:44:43 +05:30
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