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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
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
CPUs to detect that it has passed through an RCU quiescent
state. If the kernel is built with CONFIG_NO_HZ_FULL=y,