linux-kernel - Confused with CONFIG_NO_HZ and CONFIG

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Message-ID: <cf70f0210905201816g51d5d99ft35e8f33e2c470f5e@mail.gmail.com>
Date:	Wed, 20 May 2009 18:16:56 -0700
From:	Shivdas Gujare <shivdas.tech@...il.com>
To:	linux-kernel@...r.kernel.org
Subject: Confused with CONFIG_NO_HZ and CONFIG_HZ

Hi all,

I am confused with CONFIG_NO_HZ and CONFIG_HZ? What is the main
difference between it?
As per what I understood, CONFIG_NO_HZ is feature of tickless kernel,
where timer interrupts will be fired only if necessary,
and CONFIG_HZ decides the timeout of timer interrupts?

I came across description[1] from Ingo regarding CONFIG_NO_HZ as "if
there is no timer to be expired for say 1.5 seconds when
the system goes idle, then the system will stay totally idle for 1.5
seconds." then I don't understand how timer will remain unexpired
during idle if CONFIG_HZ=100,
i.e. 10ms timer timeout for timer interrupt and during such scenarios
who decides this 1.5 sec timeout.

It will be great help, if I get some more information regarding this.

Ref.
[1] http://kerneltrap.org/node/6750

Thanks and regards,
Shivdas Gujare
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