kernel/linux
0
Fork 0
mirror of https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/ synced 2026-11-08 18:57:22 +00:00
Code Issues Releases Packages Activity
No description
1,385,476 commits 117 branches 5,824 tags 6.2 GiB
  • C 96.8%
  • Assembly 0.9%
  • Rust 0.7%
  • Shell 0.6%
  • Python 0.5%
  • Other 0.3%
Find a file
Krishna Kumar 402904bfe3 net: Prevent RPS table overwrite of active flows 
[ Upstream commit 97bcc5b6f4 ]

This patch fixes an issue where two different flows on the same RXq
produce the same hash resulting in continuous flow overwrites.

Flow #1: A packet for Flow #1 comes in, kernel calls the steering
         function. The driver gives back a filter id. The kernel saves
	 this filter id in the selected slot. Later, the driver's
	 service task checks if any filters have expired and then
	 installs the rule for Flow #1.
Flow #2: A packet for Flow #2 comes in. It goes through the same steps.
         But this time, the chosen slot is being used by Flow #1. The
	 driver gives a new filter id and the kernel saves it in the
	 same slot. When the driver's service task runs, it runs through
	 all the flows, checks if Flow #1 should be expired, the kernel
	 returns True as the slot has a different filter id, and then
	 the driver installs the rule for Flow #2.
Flow #1: Another packet for Flow #1 comes in. The same thing repeats.
         The slot is overwritten with a new filter id for Flow #1.

This causes a repeated cycle of flow programming for missed packets,
wasting CPU cycles while not improving performance. This problem happens
at higher rates when the RPS table is small, but tests show it still
happens even with 12,000 connections and an RPS size of 16K per queue
(global table size = 144x16K = 64K).

This patch prevents overwriting an rps_dev_flow entry if it is active.
The intention is that it is better to do aRFS for the first flow instead
of hurting all flows on the same hash. Without this, two (or more) flows
on one RX queue with the same hash can keep overwriting each other. This
causes the driver to reprogram the flow repeatedly.

Changes:
  1. Add a new 'hash' field to struct rps_dev_flow.
  2. Add rps_flow_is_active(): a helper function to check if a flow is
     active or not, extracted from rps_may_expire_flow(). It is further
     simplified as per reviewer feedback.
  3. In set_rps_cpu():
     - Avoid overwriting by programming a new filter if:
        - The slot is not in use, or
        - The slot is in use but the flow is not active, or
        - The slot has an active flow with the same hash, but target CPU
          differs.
     - Save the hash in the rps_dev_flow entry.
  4. rps_may_expire_flow(): Use earlier extracted rps_flow_is_active().

Testing & results:
  - Driver: ice (E810 NIC), Kernel: net-next
  - #CPUs = #RXq = 144 (1:1)
  - Number of flows: 12K
  - Eight RPS settings from 256 to 32768. Though RPS=256 is not ideal,
    it is still sufficient to cover 12K flows (256*144 rx-queues = 64K
    global table slots)
  - Global Table Size = 144 * RPS (effectively equal to 256 * RPS)
  - Each RPS test duration = 8 mins (org code) + 8 mins (new code).
  - Metrics captured on client

Legend for following tables:
Steer-C: #times ndo_rx_flow_steer() was Called by set_rps_cpu()
Steer-L: #times ice_arfs_flow_steer() Looped over aRFS entries
Add:     #times driver actually programmed aRFS (ice_arfs_build_entry())
Del:     #times driver deleted the flow (ice_arfs_del_flow_rules())
Units:   K = 1,000 times, M = 1 million times

  |-------|---------|------|     Org Code    |---------|---------|
  | RPS   | Latency | CPU  | Add    |  Del   | Steer-C | Steer-L |
  |-------|---------|------|--------|--------|---------|---------|
  | 256   | 227.0   | 93.2 | 1.6M   | 1.6M   | 121.7M  | 267.6M  |
  | 512   | 225.9   | 94.1 | 11.5M  | 11.2M  | 65.7M   | 199.6M  |
  | 1024  | 223.5   | 95.6 | 16.5M  | 16.5M  | 27.1M   | 187.3M  |
  | 2048  | 222.2   | 96.3 | 10.5M  | 10.5M  | 12.5M   | 115.2M  |
  | 4096  | 223.9   | 94.1 | 5.5M   | 5.5M   | 7.2M    | 65.9M   |
  | 8192  | 224.7   | 92.5 | 2.7M   | 2.7M   | 3.0M    | 29.9M   |
  | 16384 | 223.5   | 92.5 | 1.3M   | 1.3M   | 1.4M    | 13.9M   |
  | 32768 | 219.6   | 93.2 | 838.1K | 838.1K | 965.1K  | 8.9M    |
  |-------|---------|------|   New Code      |---------|---------|
  | 256   | 201.5   | 99.1 | 13.4K  | 5.0K   | 13.7K   | 75.2K   |
  | 512   | 202.5   | 98.2 | 11.2K  | 5.9K   | 11.2K   | 55.5K   |
  | 1024  | 207.3   | 93.9 | 11.5K  | 9.7K   | 11.5K   | 59.6K   |
  | 2048  | 207.5   | 96.7 | 11.8K  | 11.1K  | 15.5K   | 79.3K   |
  | 4096  | 206.9   | 96.6 | 11.8K  | 11.7K  | 11.8K   | 63.2K   |
  | 8192  | 205.8   | 96.7 | 11.9K  | 11.8K  | 11.9K   | 63.9K   |
  | 16384 | 200.9   | 98.2 | 11.9K  | 11.9K  | 11.9K   | 64.2K   |
  | 32768 | 202.5   | 98.0 | 11.9K  | 11.9K  | 11.9K   | 64.2K   |
  |-------|---------|------|--------|--------|---------|---------|

Some observations:
  1. Overall Latency improved: (1790.19-1634.94)/1790.19*100 = 8.67%
  2. Overall CPU increased:    (777.32-751.49)/751.45*100    = 3.44%
  3. Flow Management (add/delete) remained almost constant at ~11K
     compared to values in millions.

Signed-off-by: Krishna Kumar <krikku@gmail.com>
Link: https://patch.msgid.link/20250825031005.3674864-2-krikku@gmail.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
History 2025-11-13 15:37:08 -05:00
arch s390/pci: Use pci_uevent_ers() in PCI recovery 2025-11-13 15:37:01 -05:00
block blk-cgroup: fix possible deadlock while configuring policy 2025-11-13 15:36:52 -05:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: essiv - Check ssize for decryption and in-place encryption 2025-10-19 16:37:14 +02:00
Documentation dpll: spec: add missing module-name and clock-id to pin-get reply 2025-11-13 15:36:42 -05:00
drivers drm/xe: Cancel pending TLB inval workers on teardown 2025-11-13 15:37:08 -05:00
fs virtio_fs: fix the hash table using in virtio_fs_enqueue_req() 2025-11-13 15:37:07 -05:00
include net: Prevent RPS table overwrite of active flows 2025-11-13 15:37:08 -05:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:37:27 +02:00
io_uring io_uring/zcrx: account niov arrays to cgroup 2025-11-13 15:36:51 -05:00
ipc vfs-6.17-rc1.mmap_prepare 2025-07-28 13:43:25 -07:00
kernel uprobe: Do not emulate/sstep original instruction when ip is changed 2025-11-13 15:36:53 -05:00
lib kunit: Enable PCI on UML without triggering WARN() 2025-11-13 15:36:51 -05:00
LICENSES LICENSES: Replace the obsolete address of the FSF in the GFDL-1.2 2025-07-24 11:15:39 +02:00
mm treewide: remove MIGRATEPAGE_SUCCESS 2025-10-29 14:10:32 +01:00
net net: Prevent RPS table overwrite of active flows 2025-11-13 15:37:08 -05:00
rust rust: kunit: allow cfg on tests 2025-11-13 15:36:51 -05:00
samples 15 hotfixes. 11 are cc:stable and the remainder address post-6.16 issues 2025-09-17 21:34:26 -07:00
scripts docs: kernel-doc: avoid script crash on ancient Python 2025-11-13 15:36:58 -05:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:37:28 +02:00
sound ALSA: usb-audio: Add validation of UAC2/UAC3 effect units 2025-11-13 15:37:04 -05:00
tools selftests: pci_endpoint: Skip IRQ test if IRQ is out of range. 2025-11-13 15:37:07 -05:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt Merge tag 'kvm-x86-no_assignment-6.17' of https://github.com/kvm-x86/linux into HEAD 2025-07-29 08:36:42 -04:00
.clang-format Linux 6.15-rc5 2025-05-06 16:39:25 +10:00
.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: remove trim_trailing_whitespace option 2024-06-13 16:47:52 +02:00
.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 gitignore: allow .pylintrc to be tracked 2025-07-02 17:10:04 -06:00
.mailmap 7 hotfixes. 4 are cc:stable and the remainder address post-6.16 issues or 2025-09-28 09:32:00 -07:00
.pylintrc docs: add a .pylintrc file with sys path for docs scripts 2025-04-09 12:10:33 -06:00
.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: retire Boris from TLS maintainers 2025-08-26 17:36:01 -07:00
Kbuild drm: ensure drm headers are self-contained and pass kernel-doc 2025-02-12 10:44:43 +02:00
Kconfig io_uring: Rename KConfig to Kconfig 2025-02-19 14:53:27 -07:00
MAINTAINERS i2c-for-6.17-rc8 2025-09-28 13:19:23 -07:00
Makefile Linux 6.17.7 2025-11-02 22:18:05 +09:00
README README: Fix spelling 2024-03-18 03:36:32 -06:00

README 

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the reStructuredText markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.