From: Borislav Petkov <bp@alien8.de>
To: Jonathan Corbet <corbet@lwn.net>
Cc: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Thomas Gleixner <tglx@linutronix.de>,
linux-doc@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>
Subject: [PATCH] Documentation/no_hz: Introduce "dyntick-idle mode" before using it
Date: Tue, 14 Sep 2021 22:33:55 +0200 [thread overview]
Message-ID: <20210914203355.21360-1-bp@alien8.de> (raw)
From: Borislav Petkov <bp@suse.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@suse.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
next reply other threads:[~2021-09-14 20:34 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-09-14 20:33 Borislav Petkov [this message]
2021-09-27 17:31 ` [PATCH] Documentation/no_hz: Introduce "dyntick-idle mode" before using it Jonathan Corbet
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