Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S261184AbVEQN6j (ORCPT ); Tue, 17 May 2005 09:58:39 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S261192AbVEQN6j (ORCPT ); Tue, 17 May 2005 09:58:39 -0400 Received: from mail.suse.de ([195.135.220.2]:12730 "EHLO mx1.suse.de") by vger.kernel.org with ESMTP id S261184AbVEQN6h (ORCPT ); Tue, 17 May 2005 09:58:37 -0400 Date: Tue, 17 May 2005 15:58:34 +0200 From: Andi Kleen To: Joe Korty Cc: Christoph Lameter , Linus Torvalds , randy_dunlap , akpm@osdl.org, linux-kernel@vger.kernel.org, shai@scalex86.org, ak@suse.de Subject: Re: [PATCH] i386: Selectable Frequency of the Timer Interrupt. Message-ID: <20050517135834.GG9699@wotan.suse.de> References: <20050516150907.6fde04d3.akpm@osdl.org> <20050516194651.1debabfd.rdunlap@xenotime.net> <20050517134434.GA26822@tsunami.ccur.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20050517134434.GA26822@tsunami.ccur.com> Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1144 Lines: 28 > > + help > > + 100 HZ is a typical choice for servers, SMP and NUMA systems > > + with lots of processors that may show reduced performance if > > + too many timer interrupts are occurring. > > One of the options should mention the power savings benefit on laptops. > How about: Actually it is not 100% clear. The ACPI idle code relies on the timer right now to go from C1 to C2/C3. It basically goes down in a staircase, first staying in C1, then when woken up and still idle go down lower etc. With HZ=100 the minimal latency (assuming no other interrupts) to go from C1 to C2 is 10ms, not 1ms, which might be even a power loss in some workloads. -Andi P.S.: The SUSE 2.4 kernels had for some time variable HZ, settable at boot. It surprisingly didn't cause too much slowdown or code bloat and only needed minor fixes over the tree. Might be worth considering at least as a CONFIG - 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/