linux-kernel - [PATCH] Documentation/no_hz: Introduce "dyntick-idle mode" before using it

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Date:   Tue, 14 Sep 2021 22:33:55 +0200
From:   Borislav Petkov <bp@...en8.de>
To:     Jonathan Corbet <corbet@....net>
Cc:     "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-doc@...r.kernel.org, LKML <linux-kernel@...r.kernel.org>
Subject: [PATCH] Documentation/no_hz: Introduce "dyntick-idle mode" before using it

From: Borislav Petkov <bp@...e.de>

The CONFIG_NO_HZ_IDLE paragraph is using "dyntick-idle mode" before
having defined it while the definition comes a couple of paragraphs
later.

That is leaving the reader with scratching head what that dyntick-idle
mode might be. Pull its definition up so that it is clear.

Signed-off-by: Borislav Petkov <bp@...e.de>
---
 Documentation/timers/no_hz.rst | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/Documentation/timers/no_hz.rst b/Documentation/timers/no_hz.rst
index 6cadad7c3aad..20ad23a6c618 100644
--- a/Documentation/timers/no_hz.rst
+++ b/Documentation/timers/no_hz.rst
@@ -70,6 +70,10 @@ interrupt.  After all, the primary purpose of a scheduling-clock interrupt
 is to force a busy CPU to shift its attention among multiple duties,
 and an idle CPU has no duties to shift its attention among.
 
+An idle CPU that is not receiving scheduling-clock interrupts is said to
+be "dyntick-idle", "in dyntick-idle mode", "in nohz mode", or "running
+tickless".  The remainder of this document will use "dyntick-idle mode".
+
 The CONFIG_NO_HZ_IDLE=y Kconfig option causes the kernel to avoid sending
 scheduling-clock interrupts to idle CPUs, which is critically important
 both to battery-powered devices and to highly virtualized mainframes.
@@ -91,10 +95,6 @@ Therefore, systems with aggressive real-time response constraints often
 run CONFIG_HZ_PERIODIC=y kernels (or CONFIG_NO_HZ=n for older kernels)
 in order to avoid degrading from-idle transition latencies.
 
-An idle CPU that is not receiving scheduling-clock interrupts is said to
-be "dyntick-idle", "in dyntick-idle mode", "in nohz mode", or "running
-tickless".  The remainder of this document will use "dyntick-idle mode".
-
 There is also a boot parameter "nohz=" that can be used to disable
 dyntick-idle mode in CONFIG_NO_HZ_IDLE=y kernels by specifying "nohz=off".
 By default, CONFIG_NO_HZ_IDLE=y kernels boot with "nohz=on", enabling
-- 
2.29.2