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Re-evaluating the bitmap wheight of the online cpus bitmap in every invocation of num_online_cpus() over and over is a pretty useless exercise. Especially when num_online_cpus() is used in code paths like the IPI delivery of x86 or the membarrier code. Cache the number of online CPUs in the core and just return the cached variable. The accessor function provides only a snapshot when used without protection against concurrent CPU hotplug. The storage needs to use an atomic_t because the kexec and reboot code (ab)use set_cpu_online() in their 'shutdown' handlers without any form of serialization as pointed out by Mathieu. Regular CPU hotplug usage is properly serialized. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Link: https://lkml.kernel.org/r/alpine.DEB.2.21.1907091622590.1634@nanos.tec.linutronix.de |
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arch | ||
block | ||
certs | ||
crypto | ||
Documentation | ||
drivers | ||
fs | ||
include | ||
init | ||
ipc | ||
kernel | ||
lib | ||
LICENSES | ||
mm | ||
net | ||
samples | ||
scripts | ||
security | ||
sound | ||
tools | ||
usr | ||
virt | ||
.clang-format | ||
.cocciconfig | ||
.get_maintainer.ignore | ||
.gitattributes | ||
.gitignore | ||
.mailmap | ||
COPYING | ||
CREDITS | ||
Kbuild | ||
Kconfig | ||
MAINTAINERS | ||
Makefile | ||
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.