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K Prateek Nayak ff47a0acfc sched/fair: Check idle_cpu() before need_resched() to detect ilb CPU turning busy 
Commit b2a02fc43a ("smp: Optimize send_call_function_single_ipi()")
optimizes IPIs to idle CPUs in TIF_POLLING_NRFLAG mode by setting the
TIF_NEED_RESCHED flag in idle task's thread info and relying on
flush_smp_call_function_queue() in idle exit path to run the
call-function. A softirq raised by the call-function is handled shortly
after in do_softirq_post_smp_call_flush() but the TIF_NEED_RESCHED flag
remains set and is only cleared later when schedule_idle() calls
__schedule().

need_resched() check in _nohz_idle_balance() exists to bail out of load
balancing if another task has woken up on the CPU currently in-charge of
idle load balancing which is being processed in SCHED_SOFTIRQ context.
Since the optimization mentioned above overloads the interpretation of
TIF_NEED_RESCHED, check for idle_cpu() before going with the existing
need_resched() check which can catch a genuine task wakeup on an idle
CPU processing SCHED_SOFTIRQ from do_softirq_post_smp_call_flush(), as
well as the case where ksoftirqd needs to be preempted as a result of
new task wakeup or slice expiry.

In case of PREEMPT_RT or threadirqs, although the idle load balancing
may be inhibited in some cases on the ilb CPU, the fact that ksoftirqd
is the only fair task going back to sleep will trigger a newidle balance
on the CPU which will alleviate some imbalance if it exists if idle
balance fails to do so.

Fixes: b2a02fc43a ("smp: Optimize send_call_function_single_ipi()")
Signed-off-by: K Prateek Nayak <kprateek.nayak@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/20241119054432.6405-4-kprateek.nayak@amd.com
History 2024-12-02 12:01:28 +01:00
arch i2c-for-6.13-rc1-part3 2024-12-01 13:38:24 -08:00
block block-6.13-20242901 2024-11-30 15:47:29 -08:00
certs sign-file,extract-cert: use pkcs11 provider for OPENSSL MAJOR >= 3 2024-09-20 19:52:48 +03:00
crypto Random number generator updates for Linux 6.13-rc1. 2024-11-19 10:43:44 -08:00
Documentation - Move the ->select callback to the correct ops structure in irq-mvebu-sei to 2024-12-01 12:37:58 -08:00
drivers i2c-for-6.13-rc1-part3 2024-12-01 13:38:24 -08:00
fs This pull request contains the following changes for UML: 2024-11-30 10:34:54 -08:00
include i2c-for-6.13-rc1-part3 2024-12-01 13:38:24 -08:00
init - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
io_uring io_uring-6.13-20242901 2024-11-30 15:43:02 -08:00
ipc - The series "resource: A couple of cleanups" from Andy Shevchenko 2024-11-25 16:09:48 -08:00
kernel sched/fair: Check idle_cpu() before need_resched() to detect ilb CPU turning busy 2024-12-02 12:01:28 +01:00
lib vsnprintf: Removal of bprintf() 2024-12-01 13:10:51 -08:00
LICENSES LICENSES: add 0BSD license text 2024-09-01 20:43:24 -07:00
mm Kbuild updates for v6.13 2024-11-30 13:41:50 -08:00
net 9p update for 6.13-rc1 2024-11-30 10:28:14 -08:00
rust block-6.13-20242901 2024-11-30 15:47:29 -08:00
samples TTY / Serial driver updates for 6.13-rc1 2024-11-30 09:03:16 -08:00
scripts Kbuild updates for v6.13 2024-11-30 13:41:50 -08:00
security lsm/stable-6.13 PR 20241129 2024-11-30 18:14:56 -08:00
sound sound fixes for 6.13-rc1 2024-11-29 13:01:05 -08:00
tools turbostat version 2024.11.30 2024-11-30 18:30:22 -08:00
usr initramfs: shorten cmd_initfs in usr/Makefile 2024-07-16 01:07:52 +09:00
virt VFIO updates for v6.13 2024-11-27 12:57:03 -08:00
.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: enable Clippy's check-private-items 2024-10-07 21:39:57 +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 Kbuild updates for v6.13 2024-11-30 13:41:50 -08:00
.mailmap media updates for v6.13-rc1 2024-11-20 14:01:15 -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 cgroup: Changes for v6.13 2024-11-20 09:54:49 -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 i2c-for-6.13-rc1-part3 2024-12-01 13:38:24 -08:00
Makefile Linux 6.13-rc1 2024-12-01 14:28:56 -08:00
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.