Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1757345AbZCUL5s (ORCPT ); Sat, 21 Mar 2009 07:57:48 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1752878AbZCUL5f (ORCPT ); Sat, 21 Mar 2009 07:57:35 -0400 Received: from fg-out-1718.google.com ([72.14.220.153]:35577 "EHLO fg-out-1718.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1756821AbZCUL5e (ORCPT ); Sat, 21 Mar 2009 07:57:34 -0400 Message-ID: <49C4D628.7060805@monstr.eu> Date: Sat, 21 Mar 2009 12:57:28 +0100 From: Michal Simek Reply-To: monstr@monstr.eu User-Agent: Thunderbird 2.0.0.17 (X11/20081001) MIME-Version: 1.0 To: Thomas Gleixner CC: john stultz , LKML , john.williams@petalogix.com Subject: Re: [PATCH 08/57] microblaze_v7: Interrupt handling, timer support, selfmod code References: <1237408284-8674-1-git-send-email-monstr@monstr.eu> <4b5aee01d11fc790c7842838ea63a82ee3273003.1237407249.git.monstr@monstr.eu> <5f8b2a60496983f572ef6d3b4e2f986c167a8336.1237407249.git.monstr@monstr.eu> <20fd42a1e8837c7352d35d157aa3393e88152c32.1237407249.git.monstr@monstr.eu> <49C2AB09.9040300@monstr.eu> <1237515861.7106.215.camel@jstultz-laptop> <49C34558.6030006@monstr.eu> <1237581607.7191.51.camel@localhost.localdomain> <49C4C3BD.9090905@monstr.eu> In-Reply-To: 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 Content-Length: 1772 Lines: 48 Thomas Gleixner wrote: > On Sat, 21 Mar 2009, Michal Simek wrote: >> CONFIG_HZ_100=y >> # CONFIG_HZ_250 is not set >> # CONFIG_HZ_300 is not set >> # CONFIG_HZ_1000 is not set >> CONFIG_HZ=100 >> >> For NO_HZ val I shouldn't use HZ value because of NO_HZ and HZ values shouldn't >> be in .config file. Am I right? > > No. NO_HZ does not remove the HZ value from the kernel. There is way > too much code depending on it. What NO_HZ does is to supress the > periodic tick when the system goes idle and the next timer expiry is > farther away than 1 HZ. When the system is non idle then the periodic > tick runs again. NO_HZ is merily for power saving. > > In a normal kernel when the machine is idle then we wake up every HZ > to find out that there is no work to do and we go idle again. But if > you think about it then this is stupid, because the kernel knows when > the next timer is due to expire. So if the next timer expiry is > e.g. 100ms away, then we can sleep for full 100ms instead of sleeping > 10 * 10ms (HZ=100) or 100 * 1ms (HZ=1000). This allows systems to go > into deeper power saving states. > > You should be able to observe the difference by monitoring > /proc/interrupts. A nohz enabled kernel should have significantly less > timer interrupts on an idle system. Yes, I see it. I think I sent my log in any previous email in this thread too + I see it on my heartbeat led too. Thanks for explanation, Michal > > Thanks, > > tglx -- Michal Simek, Ing. (M.Eng) w: www.monstr.eu p: +42-0-721842854 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/