Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758476AbZD1Va6 (ORCPT ); Tue, 28 Apr 2009 17:30:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1754379AbZD1Vas (ORCPT ); Tue, 28 Apr 2009 17:30:48 -0400 Received: from smtp.ultrahosting.com ([74.213.174.254]:53976 "EHLO smtp.ultrahosting.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751315AbZD1Var (ORCPT ); Tue, 28 Apr 2009 17:30:47 -0400 Date: Tue, 28 Apr 2009 17:21:29 -0400 (EDT) From: Christoph Lameter X-X-Sender: cl@qirst.com To: Peter Zijlstra cc: Pavel Machek , Ingo Molnar , linux-kernel@vger.kernel.org Subject: Re: Scheduler regression: Too frequent timer interrupts(?) In-Reply-To: <1240953796.7620.160.camel@twins> Message-ID: References: <1239951613.23397.4107.camel@laptop> <1239977776.23397.4590.camel@laptop> <1239979901.23397.4638.camel@laptop> <1239982137.23397.4684.camel@laptop> <20090423044228.GA2428@ucw.cz> <1240953796.7620.160.camel@twins> User-Agent: Alpine 1.10 (DEB 962 2008-03-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1264 Lines: 35 On Tue, 28 Apr 2009, Peter Zijlstra wrote: > On Tue, 2009-04-28 at 17:02 -0400, Christoph Lameter wrote: > > On Thu, 23 Apr 2009, Pavel Machek wrote: > > > > > I'd say that taking interrupt and returning in below 1000nsec is > > > impossible, even on very fast hw. > > > > Hmmm.... Could it be that CONFIG_NO_HZ caused the timer interrupt to be > > avoided in earlier releases? NO_HZ theory at least is to only schedule > > interrupts when necessary. So an interrupt is needed at the end of the > > scheduling intervals and not at HZ frequency. > > No, NOHZ only works on idle cpus. It is advertised to do more: config NO_HZ bool "Tickless System (Dynamic Ticks)" depends on GENERIC_TIME && GENERIC_CLOCKEVENTS select TICK_ONESHOT help This option enables a tickless system: timer interrupts will only trigger on an as-needed basis both when the system is busy and when the system is idle. So NO_HZ is really IDLE_NO_HZ. The system is not tickless. -- 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/