github-mirror/linux
1
0
Fork 0
mirror of https://github.com/torvalds/linux.git synced 2026-07-31 19:47:08 +02:00
Code Issues Actions Packages Projects Releases Wiki Activity Graph
Linux kernel source tree
1,368,889 Commits 1 Branch 940 Tags 24 GiB
C 96.9%
Assembly 0.9%
Rust 0.6%
Shell 0.6%
Python 0.5%
Other 0.3%
114a2de6fa
Go to file
Anthoine Bourgeois 114a2de6fa xen/netfront: Fix TX response spurious interrupts 
We found at Vates that there are lot of spurious interrupts when
benchmarking the xen-net PV driver frontend. This issue appeared with a
patch that addresses security issue XSA-391 (b27d47950e "xen/netfront:
harden netfront against event channel storms"). On an iperf benchmark,
spurious interrupts can represent up to 50% of the interrupts.

Spurious interrupts are interrupts that are rised for nothing, there is
no work to do. This appends because the function that handles the
interrupts ("xennet_tx_buf_gc") is also called at the end of the request
path to garbage collect the responses received during the transmission
load.

The request path is doing the work that the interrupt handler should
have done otherwise. This is particurary true when there is more than
one vcpu and get worse linearly with the number of vcpu/queue.

Moreover, this problem is amplifyed by the penalty imposed by a spurious
interrupt. When an interrupt is found spurious the interrupt chip will
delay the EOI to slowdown the backend. This delay will allow more
responses to be handled by the request path and then there will be more
chance the next interrupt will not find any work to do, creating a new
spurious interrupt.

This causes performance issue. The solution here is to remove the calls
from the request path and let the interrupt handler do the processing of
the responses. This approch removes most of the spurious interrupts
(<0.05%) and also has the benefit of freeing up cycles in the request
path, allowing it to process more work, which improves performance
compared to masking the spurious interrupt one way or another.

This optimization changes a part of the code that is present since the
net frontend driver was upstreamed. There is no similar pattern in the
other xen PV drivers. Since the first commit of xen-netfront is a blob
that doesn't explain all the design choices I can only guess why this
specific mecanism was here. This could have been introduce to compensate
a slow backend at the time (maybe the backend was fixed or optimize
later) or a small queue. In 18 years, both frontend and backend gain lot
of features and optimizations that could have obsolete the feature of
reaping completions from the TX path.

Some vif throughput performance figures from a 8 vCPUs, 4GB of RAM HVM
guest(s):

Without this patch on the :
vm -> dom0: 4.5Gb/s
vm -> vm:   7.0Gb/s

Without XSA-391 patch (revert of b27d47950e):
vm -> dom0: 8.3Gb/s
vm -> vm:   8.7Gb/s

With XSA-391 and this patch:
vm -> dom0: 11.5Gb/s
vm -> vm:   12.6Gb/s

v2:
- add revewed and tested by tags
- resend with the maintainers in the recipients list

v3:
- remove Fixes tag but keep the commit ref in the explanation
- add a paragraph on why this code was here

Signed-off-by: Anthoine Bourgeois <anthoine.bourgeois@vates.tech>
Reviewed-by: Juergen Gross <jgross@suse.com>
Tested-by: Elliott Mitchell <ehem+xen@m5p.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20250721093316.23560-1-anthoine.bourgeois@vates.tech>
2025-07-23 13:11:03 +02:00
arch - Update Kirill's email address 2025-07-13 10:41:19 -07:00
block block-6.16-20250626 2025-06-27 09:02:33 -07:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto crypto: wp512 - Use API partial block handling 2025-06-23 16:56:56 +08:00
Documentation Fixes for a few clk drivers and bindings: 2025-07-13 11:37:35 -07:00
drivers xen/netfront: Fix TX response spurious interrupts 2025-07-23 13:11:03 +02:00
fs 19 hotfixes. A whopping 16 are cc:stable and the remainder address 2025-07-12 10:30:47 -07:00
include xen: Remove some deadcode (x) 2025-07-14 09:55:52 +02:00
init futex: Temporary disable FUTEX_PRIVATE_HASH 2025-07-01 15:02:05 +02:00
io_uring io_uring-6.16-20250710 2025-07-11 10:29:30 -07:00
ipc - The 3 patch series "hung_task: extend blocking task stacktrace dump to 2025-05-31 19:12:53 -07:00
kernel - Prevent perf_sigtrap() from observing an exiting task and warning 2025-07-13 10:34:47 -07:00
lib maple_tree: fix mt_destroy_walk() on root leaf node 2025-07-09 21:07:52 -07:00
LICENSES LICENSES: add CC0-1.0 license text 2025-05-21 14:54:17 +02:00
mm Revert "sched/numa: add statistics of numa balance task" 2025-07-09 21:07:56 -07:00
net netlink: make sure we allow at least one dump skb 2025-07-11 07:31:47 -07:00
rust Merge tag 'drm-misc-fixes-2025-07-10' of https://gitlab.freedesktop.org/drm/misc/kernel into drm-fixes 2025-07-11 14:11:19 +02:00
samples samples/damon: fix damon sample mtier for start failure 2025-07-09 21:07:55 -07:00
scripts scripts: gdb: vfs: support external dentry names 2025-07-09 21:07:54 -07:00
security selinux: change security_compute_sid to return the ssid or tsid on match 2025-06-19 16:13:16 -04:00
sound ALSA: hda/realtek: Enable headset Mic on Positivo K116J 2025-07-07 14:09:09 +02:00
tools - Update Kirill's email address 2025-07-13 10:41:19 -07:00
usr usr/include: openrisc: don't HDRTEST bpf_perf_event.h 2025-05-12 15:03:17 +09:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-06-24 12:20:17 -07:00
.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: Retire Ralf Baechle 2024-11-12 15:48:59 +01:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore .gitignore: ignore Python compiled bytecode 2025-04-24 10:12:46 -06:00
.mailmap MAINTAINERS: Update Kirill Shutemov's email address for TDX 2025-07-11 07:25:51 -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 CREDITS: Add entry for Shannon Nelson 2025-06-21 07:34:28 -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 - Update Kirill's email address 2025-07-13 10:41:19 -07:00
Makefile Linux 6.16-rc6 2025-07-13 14:25:58 -07:00
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.