From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755578AbZEUBYR (ORCPT ); Wed, 20 May 2009 21:24:17 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752950AbZEUBYK (ORCPT ); Wed, 20 May 2009 21:24:10 -0400 Received: from qw-out-2122.google.com ([74.125.92.26]:43944 "EHLO qw-out-2122.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752341AbZEUBYJ (ORCPT ); Wed, 20 May 2009 21:24:09 -0400 DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=mime-version:date:message-id:subject:from:to:content-type :content-transfer-encoding; b=IOwEAvNpQbSJ6a/ql8vZUuDpjqXHyFDPS1VbTb2zwo2uWhNXG6dTKISNvoKi0jcEgq P1mPfpZdoTCc/kFyjiumm7SJV9BU7UqPwx2+jN7E6adEvjNESY3UOG8TtQKcrlw+gQs7 pvOmVxa+t43aTPZR/jsk+ciDqJcxSrpnF4IJA= MIME-Version: 1.0 Date: Wed, 20 May 2009 18:16:56 -0700 Message-ID: Subject: Confused with CONFIG_NO_HZ and CONFIG_HZ From: Shivdas Gujare To: linux-kernel@vger.kernel.org Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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