From: "Paul E. McKenney" <paulmck@kernel.org>
To: rcu@vger.kernel.org
Cc: linux-kernel@vger.kernel.org, kernel-team@fb.com,
mingo@kernel.org, jiangshanlai@gmail.com,
akpm@linux-foundation.org, mathieu.desnoyers@efficios.com,
josh@joshtriplett.org, tglx@linutronix.de, peterz@infradead.org,
rostedt@goodmis.org, dhowells@redhat.com, edumazet@google.com,
fweisbec@gmail.com, oleg@redhat.com, joel@joelfernandes.org,
"Paul E. McKenney" <paulmck@kernel.org>
Subject: [PATCH rcu 1/3] doc: Remove obsolete kernel-per-CPU-kthreads RCU_FAST_NO_HZ advice
Date: Wed, 1 Dec 2021 16:06:40 -0800 [thread overview]
Message-ID: <20211202000642.3126064-1-paulmck@kernel.org> (raw)
In-Reply-To: <20211202000540.GA3125972@paulmck-ThinkPad-P17-Gen-1>
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>
---
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
next prev parent reply other threads:[~2021-12-02 0:08 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-12-02 0:05 [PATCH rcu 0/3] Documentation updates for v5.17 Paul E. McKenney
2021-12-02 0:06 ` Paul E. McKenney [this message]
2021-12-02 0:06 ` [PATCH rcu 2/3] doc: Add refcount analogy to What is RCU Paul E. McKenney
2021-12-02 0:06 ` [PATCH rcu 3/3] doc: RCU: Avoid 'Symbol' font-family in SVG figures Paul E. McKenney
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