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Message-Id: <20211202000642.3126064-1-paulmck@kernel.org>
Date: Wed, 1 Dec 2021 16:06:40 -0800
From: "Paul E. McKenney" <paulmck@...nel.org>
To: rcu@...r.kernel.org
Cc: linux-kernel@...r.kernel.org, kernel-team@...com, mingo@...nel.org,
jiangshanlai@...il.com, akpm@...ux-foundation.org,
mathieu.desnoyers@...icios.com, josh@...htriplett.org,
tglx@...utronix.de, peterz@...radead.org, rostedt@...dmis.org,
dhowells@...hat.com, edumazet@...gle.com, fweisbec@...il.com,
oleg@...hat.com, joel@...lfernandes.org,
"Paul E. McKenney" <paulmck@...nel.org>
Subject: [PATCH rcu 1/3] doc: Remove obsolete kernel-per-CPU-kthreads RCU_FAST_NO_HZ advice
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@...nel.org>
---
Documentation/admin-guide/kernel-per-CPU-kthreads.rst | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)
diff --git a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst
index 5e51ee5b03589..e4a5fc26f1a9d 100644
--- a/Documentation/admin-guide/kernel-per-CPU-kthreads.rst
+++ b/Documentation/admin-guide/kernel-per-CPU-kthreads.rst
@@ -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,
--
2.31.1.189.g2e36527f23
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