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Thomas Gleixner 2452483d95 Revert "lib: Restrict cpumask_local_spread to houskeeping CPUs" 
This reverts commit 1abdfe706a.

This change is broken and not solving any problem it claims to solve.

Robin reported that cpumask_local_spread() now returns any cpu out of
cpu_possible_mask in case that NOHZ_FULL is disabled (runtime or compile
time). It can also return any offline or not-present CPU in the
housekeeping mask. Before that it was returning a CPU out of
online_cpu_mask.

While the function is racy against CPU hotplug if the caller does not
protect against it, the actual use cases are not caring much about it as
they use it mostly as hint for:

 - the user space affinity hint which is unused by the kernel
 - memory node selection which is just suboptimal
 - network queue affinity which might fail but is handled gracefully

But the occasional fail vs. hotplug is very different from returning
anything from possible_cpu_mask which can have a large amount of offline
CPUs obviously.

The changelog of the commit claims:

 "The current implementation of cpumask_local_spread() does not respect
  the isolated CPUs, i.e., even if a CPU has been isolated for Real-Time
  task, it will return it to the caller for pinning of its IRQ
  threads. Having these unwanted IRQ threads on an isolated CPU adds up
  to a latency overhead."

The only correct part of this changelog is:

 "The current implementation of cpumask_local_spread() does not respect
  the isolated CPUs."

Everything else is just disjunct from reality.

Reported-by: Robin Murphy <robin.murphy@arm.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Cc: Nitesh Narayan Lal <nitesh@redhat.com>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: abelits@marvell.com
Cc: davem@davemloft.net
Link: https://lore.kernel.org/r/87y2g26tnt.fsf@nanos.tec.linutronix.de
2021-02-05 23:28:29 +01:00
arch A single fix for objtool to generate proper unwind info for newer 2021-01-31 11:48:12 -08:00
block block-5.11-2021-01-29 2021-01-29 13:50:06 -08:00
certs .gitignore: add SPDX License Identifier 2020-03-25 11:50:48 +01:00
crypto X.509: Fix crash caused by NULL pointer 2021-01-20 11:33:51 -08:00
Documentation A single fix for objtool to generate proper unwind info for newer 2021-01-31 11:48:12 -08:00
drivers A single EFI fix from Lukas: 2021-01-31 11:57:37 -08:00
fs NFS client bugfixes for Linux 5.11 2021-01-31 11:19:12 -08:00
include A single fix for objtool to generate proper unwind info for newer 2021-01-31 11:48:12 -08:00
init Revert "init/console: Use ttynull as a fallback when there is no console" 2021-01-08 11:02:18 -08:00
ipc Merge branch 'akpm' (patches from Andrew) 2020-12-15 12:53:37 -08:00
kernel A single fix for the single step reporting regression caused by getting the 2021-01-31 11:39:32 -08:00
lib Revert "lib: Restrict cpumask_local_spread to houskeeping CPUs" 2021-02-05 23:28:29 +01:00
LICENSES LICENSES: Add the CC-BY-4.0 license 2020-12-08 10:33:27 -07:00
mm Revert "mm/slub: fix a memory leak in sysfs_slab_add()" 2021-01-28 09:05:44 -08:00
net NFS client bugfixes for Linux 5.11 2021-01-31 11:19:12 -08:00
samples ARM: SoC drivers for v5.11 2020-12-16 16:38:41 -08:00
scripts Kbuild fixes for v5.11 2021-01-10 13:24:55 -08:00
security dump_common_audit_data(): fix racy accesses to ->d_name 2021-01-16 15:11:35 -05:00
sound ALSA: hda/via: Apply the workaround generically for Clevo machines 2021-01-26 18:05:03 +01:00
tools Networking fixes for 5.11-rc6, including fixes from can, xfrm, wireless, 2021-01-28 15:24:43 -08:00
usr Merge branch 'work.fdpic' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2020-08-07 13:29:39 -07:00
virt KVM/arm64 fixes for 5.11, take #2 2021-01-25 18:52:01 -05:00
.clang-format RDMA 5.10 pull request 2020-10-17 11:18:18 -07:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore Opt out of scripts/get_maintainer.pl 2019-05-16 10:53:40 -07:00
.gitattributes .gitattributes: use 'dts' diff driver for dts files 2019-12-04 19:44:11 -08:00
.gitignore .gitignore: docs: ignore sphinx_*/ directories 2020-09-10 10:44:31 -06:00
.mailmap mailmap: remove the "repo-abbrev" comment 2021-01-26 11:40:17 -08:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: dccp: move Gerrit Renker to CREDITS 2021-01-14 10:53:49 -08:00
Kbuild kbuild: rename hostprogs-y/always to hostprogs/always-y 2020-02-04 01:53:07 +09:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS Networking fixes for 5.11-rc6, including fixes from can, xfrm, wireless, 2021-01-28 15:24:43 -08:00
Makefile Linux 5.11-rc6 2021-01-31 13:50:09 -08:00
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.