2452483d95
This reverts commit 1abdfe706a579a702799fce465bceb9fb01d407c. 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
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.