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Linus Torvalds ff887eb07c workqueue: Changes for v6.9 This cycle, a lot of workqueue changes including some that are significant and invasive. - During v6.6 cycle, unbound workqueues were updated so that they are more topology aware and flexible, which among other things improved workqueue behavior on modern multi-L3 CPUs. In the process, `636b927eba` ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues") switched unbound workqueues to use per-CPU frontend pool_workqueues as a part of increasing front-back mapping flexibility. An unwelcome side effect of this change was that this made max concurrency enforcement per-CPU blowing up the maximum number of allowed concurrent executions. I incorrectly assumed that this wouldn't cause practical problems as most unbound workqueue users are self-regulate max concurrency; however, there definitely are which don't (e.g. on IO paths) and the drastic increase in the allowed max concurrency led to noticeable perf regressions in some use cases. This is now addressed by separating out max concurrency enforcement to a separate struct - wq_node_nr_active - which makes @max_active consistently mean system-wide max concurrency regardless of the number of CPUs or (finally) NUMA nodes. This is a rather invasive and, in places, a bit clunky; however, the clunkiness rises from the the inherent requirement to handle the disagreement between the execution locality domain and max concurrency enforcement domain on some modern machines. See `5797b1c189` ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues") for more details. - BH workqueue support is added. They are similar to per-CPU workqueues but execute work items in the softirq context. This is expected to replace tasklet. However, currently, it's missing the ability to disable and enable work items which is needed to convert many tasklet users. To avoid crowding this merge window too much, this will be included in the next merge window. A separate pull request will be sent for the couple conversion patches that are currently pending. - Waiman plugged a long-standing hole in workqueue CPU isolation where ordered workqueues didn't follow wq_unbound_cpumask updates. Ordered workqueues now follow the same rules as other unbound workqueues. - More CPU isolation improvements: Juri fixed another deficit in workqueue isolation where unbound rescuers don't respect wq_unbound_cpumask. Leonardo fixed delayed_work timers firing on isolated CPUs. - Other misc changes. -----BEGIN PGP SIGNATURE----- iIQEABYKACwWIQTfIjM1kS57o3GsC/uxYfJx3gVYGQUCZe7JCQ4cdGpAa2VybmVs Lm9yZwAKCRCxYfJx3gVYGcnqAP9UP8zEM1la19cilhboDumxmRWyRpV/egFOqsMP Y5PuoAEAtsBJtQWtm5w46+y+fk3nK2ugXlQio2gH0qQcxX6SdgQ= =/ovv -----END PGP SIGNATURE----- Merge tag 'wq-for-6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq Pull workqueue updates from Tejun Heo: "This cycle, a lot of workqueue changes including some that are significant and invasive. - During v6.6 cycle, unbound workqueues were updated so that they are more topology aware and flexible, which among other things improved workqueue behavior on modern multi-L3 CPUs. In the process, commit `636b927eba` ("workqueue: Make unbound workqueues to use per-cpu pool_workqueues") switched unbound workqueues to use per-CPU frontend pool_workqueues as a part of increasing front-back mapping flexibility. An unwelcome side effect of this change was that this made max concurrency enforcement per-CPU blowing up the maximum number of allowed concurrent executions. I incorrectly assumed that this wouldn't cause practical problems as most unbound workqueue users are self-regulate max concurrency; however, there definitely are which don't (e.g. on IO paths) and the drastic increase in the allowed max concurrency led to noticeable perf regressions in some use cases. This is now addressed by separating out max concurrency enforcement to a separate struct - wq_node_nr_active - which makes @max_active consistently mean system-wide max concurrency regardless of the number of CPUs or (finally) NUMA nodes. This is a rather invasive and, in places, a bit clunky; however, the clunkiness rises from the the inherent requirement to handle the disagreement between the execution locality domain and max concurrency enforcement domain on some modern machines. See commit `5797b1c189` ("workqueue: Implement system-wide nr_active enforcement for unbound workqueues") for more details. - BH workqueue support is added. They are similar to per-CPU workqueues but execute work items in the softirq context. This is expected to replace tasklet. However, currently, it's missing the ability to disable and enable work items which is needed to convert many tasklet users. To avoid crowding this merge window too much, this will be included in the next merge window. A separate pull request will be sent for the couple conversion patches that are currently pending. - Waiman plugged a long-standing hole in workqueue CPU isolation where ordered workqueues didn't follow wq_unbound_cpumask updates. Ordered workqueues now follow the same rules as other unbound workqueues. - More CPU isolation improvements: Juri fixed another deficit in workqueue isolation where unbound rescuers don't respect wq_unbound_cpumask. Leonardo fixed delayed_work timers firing on isolated CPUs. - Other misc changes" * tag 'wq-for-6.9' of git://git.kernel.org/pub/scm/linux/kernel/git/tj/wq: (54 commits) workqueue: Drain BH work items on hot-unplugged CPUs workqueue: Introduce from_work() helper for cleaner callback declarations workqueue: Control intensive warning threshold through cmdline workqueue: Make @flags handling consistent across set_work_data() and friends workqueue: Remove clear_work_data() workqueue: Factor out work_grab_pending() from __cancel_work_sync() workqueue: Clean up enum work_bits and related constants workqueue: Introduce work_cancel_flags workqueue: Use variable name irq_flags for saving local irq flags workqueue: Reorganize flush and cancel[_sync] functions workqueue: Rename __cancel_work_timer() to __cancel_timer_sync() workqueue: Use rcu_read_lock_any_held() instead of rcu_read_lock_held() workqueue: Cosmetic changes workqueue, irq_work: Build fix for !CONFIG_IRQ_WORK workqueue: Fix queue_work_on() with BH workqueues async: Use a dedicated unbound workqueue with raised min_active workqueue: Implement workqueue_set_min_active() workqueue: Fix kernel-doc comment of unplug_oldest_pwq() workqueue: Bind unbound workqueue rescuer to wq_unbound_cpumask kernel/workqueue: Let rescuers follow unbound wq cpumask changes ...		2024-03-11 12:50:42 -07:00
arch	for-6.9/block-20240310	2024-03-11 11:43:44 -07:00
block	for-6.9/block-20240310	2024-03-11 11:43:44 -07:00
certs	This update includes the following changes:	2023-11-02 16:15:30 -10:00
crypto	crypto: lskcipher - Copy IV in lskcipher glue code always	2024-02-24 08:37:24 +08:00
Documentation	workqueue: Changes for v6.9	2024-03-11 12:50:42 -07:00
drivers	for-6.9/block-20240310	2024-03-11 11:43:44 -07:00
fs	for-6.9/block-20240310	2024-03-11 11:43:44 -07:00
include	workqueue: Changes for v6.9	2024-03-11 12:50:42 -07:00
init	workqueue: Changes for v6.9	2024-03-11 12:50:42 -07:00
io_uring	for-6.9/io_uring-20240310	2024-03-11 11:35:31 -07:00
ipc	shm: Slim down dependencies	2023-12-20 19:26:31 -05:00
kernel	workqueue: Changes for v6.9	2024-03-11 12:50:42 -07:00
lib	vfs-6.9.misc	2024-03-11 09:38:17 -07:00
LICENSES	LICENSES: Add the copyleft-next-0.3.1 license	2022-11-08 15:44:01 +01:00
mm	vfs-6.9.uuid	2024-03-11 11:02:06 -07:00
net	for-6.9/io_uring-20240310	2024-03-11 11:35:31 -07:00
rust	workqueue: Changes for v6.9	2024-03-11 12:50:42 -07:00
samples	work around gcc bugs with 'asm goto' with outputs	2024-02-09 15:57:48 -08:00
scripts	Rust changes for v6.9	2024-03-11 12:31:28 -07:00
security	integrity-v6.8-fix	2024-03-05 13:21:30 -08:00
sound	ASoC: Fixes for v6.8	2024-03-08 08:53:36 +01:00
tools	workqueue: Changes for v6.9	2024-03-11 12:50:42 -07:00
usr	Kbuild updates for v6.8	2024-01-18 17:57:07 -08:00
virt	KVM: Make KVM_MEM_GUEST_MEMFD mutually exclusive with KVM_MEM_READONLY	2024-02-22 17:07:06 -08:00
.clang-format	clang-format: Update with v6.7-rc4's `for_each` macro list	2023-12-08 23:54:38 +01:00
.cocciconfig
.editorconfig	Add .editorconfig file for basic formatting	2023-12-28 16:22:47 +09:00
.get_maintainer.ignore	get_maintainer: add Alan to .get_maintainer.ignore	2022-08-20 15:17:44 -07:00
.gitattributes	.gitattributes: set diff driver for Rust source code files	2023-05-31 17:48:25 +02:00
.gitignore	Add .editorconfig file for basic formatting	2023-12-28 16:22:47 +09:00
.mailmap	drm fixes for 6.8 final	2024-03-08 12:44:56 -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	vfs-6.9.ntfs	2024-03-11 09:55:17 -07:00
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	vfs-6.9.ntfs	2024-03-11 09:55:17 -07:00
Makefile	Rust changes for v6.9	2024-03-11 12:31:28 -07:00
README	Drop all 00-INDEX files from Documentation/	2018-09-09 15:08:58 -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 Restructured Text 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.