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Jens Axboe c0325d6892 io_uring/sqpoll: be smarter on when to update the stime usage 
Commit a94e065726 upstream.

The current approach is a bit naive, and hence calls the time querying
way too often. Only start the "doing work" timer when there's actual
work to do, and then use that information to terminate (and account) the
work time once done. This greatly reduces the frequency of these calls,
when they cannot have changed anyway.

Running a basic random reader that is setup to use SQPOLL, a profile
before this change shows these as the top cycle consumers:

+   32.60%  iou-sqp-1074  [kernel.kallsyms]  [k] thread_group_cputime_adjusted
+   19.97%  iou-sqp-1074  [kernel.kallsyms]  [k] thread_group_cputime
+   12.20%  io_uring      io_uring           [.] submitter_uring_fn
+    4.13%  iou-sqp-1074  [kernel.kallsyms]  [k] getrusage
+    2.45%  iou-sqp-1074  [kernel.kallsyms]  [k] io_submit_sqes
+    2.18%  iou-sqp-1074  [kernel.kallsyms]  [k] __pi_memset_generic
+    2.09%  iou-sqp-1074  [kernel.kallsyms]  [k] cputime_adjust

and after this change, top of profile looks as follows:

+   36.23%  io_uring     io_uring           [.] submitter_uring_fn
+   23.26%  iou-sqp-819  [kernel.kallsyms]  [k] io_sq_thread
+   10.14%  iou-sqp-819  [kernel.kallsyms]  [k] io_sq_tw
+    6.52%  iou-sqp-819  [kernel.kallsyms]  [k] tctx_task_work_run
+    4.82%  iou-sqp-819  [kernel.kallsyms]  [k] nvme_submit_cmds.part.0
+    2.91%  iou-sqp-819  [kernel.kallsyms]  [k] io_submit_sqes
[...]
     0.02%  iou-sqp-819  [kernel.kallsyms]  [k] cputime_adjust

where it's spending the cycles on things that actually matter.

Reported-by: Fengnan Chang <changfengnan@bytedance.com>
Cc: stable@vger.kernel.org
Fixes: 3fcb9d1720 ("io_uring/sqpoll: statistics of the true utilization of sq threads")
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
History 2025-10-29 14:08:59 +01:00
arch riscv: hwprobe: avoid uninitialized variable use in hwprobe_arch_id() 2025-10-29 14:08:59 +01:00
block blk-crypto: fix missing blktrace bio split events 2025-10-19 16:33:48 +02:00
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 16:33:42 +02:00
Documentation arm64: errata: Apply workarounds for Neoverse-V3AE 2025-10-23 16:20:47 +02:00
drivers gpio: ljca: Fix duplicated IRQ mapping 2025-10-29 14:08:59 +01:00
fs ocfs2: clear extent cache after moving/defragmenting extents 2025-10-29 14:08:57 +01:00
include mm/ksm: fix flag-dropping behavior in ksm_madvise 2025-10-23 16:20:47 +02:00
init init: handle bootloader identifier in kernel parameters 2025-10-19 16:33:50 +02:00
io_uring io_uring/sqpoll: be smarter on when to update the stime usage 2025-10-29 14:08:59 +01:00
ipc ipc: fix to protect IPCS lookups using RCU 2025-06-27 11:11:22 +01:00
kernel sched: Remove never used code in mm_cid_get() 2025-10-29 14:08:59 +01:00
lib lib/crypto/curve25519-hacl64: Disable KASAN with clang-17 and older 2025-10-19 16:34:00 +02:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm mm: prevent poison consumption when splitting THP 2025-10-29 14:08:57 +01:00
net vsock: fix lock inversion in vsock_assign_transport() 2025-10-29 14:08:57 +01:00
rust mm/ksm: fix flag-dropping behavior in ksm_madvise 2025-10-23 16:20:47 +02:00
samples ftrace/samples: Fix function size computation 2025-09-19 16:35:44 +02:00
scripts gcc-plugins: Remove TODO_verify_il for GCC >= 16 2025-10-06 11:17:52 +02:00
security KEYS: trusted_tpm1: Compare HMAC values in constant time 2025-10-19 16:33:51 +02:00
sound ASoC: amd/sdw_utils: avoid NULL deref when devm_kasprintf() fails 2025-10-23 16:20:37 +02:00
tools selftests: mptcp: join: mark implicit tests as skipped if not supported 2025-10-29 14:08:57 +01:00
usr kbuild: hdrcheck: fix cross build with clang 2025-03-13 13:02:18 +01:00
virt KVM: Allow CPU to reschedule while setting per-page memory attributes 2025-07-17 18:37:08 +02:00
.clang-format clang-format: Update with v6.11-rc1's for_each macro list 2024-08-02 13:20:31 +02:00
.clippy.toml rust: give Clippy the minimum supported Rust version 2025-08-01 09:48:44 +01:00
.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 Add Jeff Kirsher to .get_maintainer.ignore 2024-03-08 11:36:54 +00:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore rust: introduce .clippy.toml 2025-03-13 13:01:42 +01:00
.mailmap mailmap: add entry for Thorsten Blum 2024-11-07 14:14:59 -08:00
.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 self from DSA entry 2024-11-03 12:52:38 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: Update Alexey Makhalov's email address 2025-05-22 14:29:46 +02:00
Makefile Unbreak 'make tools/*' for user-space targets 2025-10-29 14:08:53 +01:00
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.