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doc: Remove obsolete kernel-per-CPU-kthreads RCU_FAST_NO_HZ advice

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This document advises building with both CONFIG_NO_HZ=y and
CONFIG_RCU_FAST_NO_HZ=y.  However, CONFIG_NO_HZ=y offloads callbacks from
all nohz_full CPUs, and CPUs with offloaded callbacks do not benefit from
CONFIG_RCU_FAST_NO_HZ=y.  Quite the opposite: CONFIG_RCU_FAST_NO_HZ=y
simply adds a bit of idle entry/exit overhead.

This commit therefore changes that advice to only CONFIG_NO_HZ=y.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2021-09-27 10:54:22 -07:00
parent 8c0abfd6d2
commit db4cb76861
1 changed files with 1 additions and 1 deletions
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2
Documentation/admin-guide/kernel-per-CPU-kthreads.rst
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@ -208,7 +208,7 @@ Do at least one of the following:
2. Enable RCU to do its processing remotely via dyntick-idle by 2. Enable RCU to do its processing remotely via dyntick-idle by
doing all of the following: doing all of the following:
a. Build with CONFIG_NO_HZ=y and CONFIG_RCU_FAST_NO_HZ=y. a. Build with CONFIG_NO_HZ=y.
b. Ensure that the CPU goes idle frequently, allowing other b. Ensure that the CPU goes idle frequently, allowing other
CPUs to detect that it has passed through an RCU quiescent CPUs to detect that it has passed through an RCU quiescent
state. If the kernel is built with CONFIG_NO_HZ_FULL=y, state. If the kernel is built with CONFIG_NO_HZ_FULL=y,