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Documentation/no_hz: Introduce "dyntick-idle mode" before using it

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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>
Link: https://lore.kernel.org/r/20210914203355.21360-1-bp@alien8.de
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
This commit is contained in:
Borislav Petkov 2021-09-14 22:33:55 +02:00 committed by Jonathan Corbet
parent 9770a13265
commit 15ce51f55e
1 changed files with 4 additions and 4 deletions
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8
Documentation/timers/no_hz.rst
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@ -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, 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. 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 The CONFIG_NO_HZ_IDLE=y Kconfig option causes the kernel to avoid sending
scheduling-clock interrupts to idle CPUs, which is critically important scheduling-clock interrupts to idle CPUs, which is critically important
both to battery-powered devices and to highly virtualized mainframes. 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) run CONFIG_HZ_PERIODIC=y kernels (or CONFIG_NO_HZ=n for older kernels)
in order to avoid degrading from-idle transition latencies. 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 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". 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 By default, CONFIG_NO_HZ_IDLE=y kernels boot with "nohz=on", enabling