From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758909AbZEEVo6 (ORCPT ); Tue, 5 May 2009 17:44:58 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1753655AbZEEVor (ORCPT ); Tue, 5 May 2009 17:44:47 -0400 Received: from earthlight.etchedpixels.co.uk ([81.2.110.250]:38879 "EHLO www.etchedpixels.co.uk" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1758483AbZEEVor (ORCPT ); Tue, 5 May 2009 17:44:47 -0400 Date: Tue, 5 May 2009 22:44:17 +0100 From: Alan Cox To: "H. Peter Anvin" Cc: akataria@vmware.com, Ingo Molnar , Thomas Gleixner , the arch/x86 maintainers , LKML Subject: Re: [PATCH] x86: Reduce the default HZ value Message-ID: <20090505224417.0f00c2f0@lxorguk.ukuu.org.uk> In-Reply-To: <4A00ADDE.9000908@zytor.com> References: <1241462661.412.8.camel@alok-dev1> <4A00ADDE.9000908@zytor.com> X-Mailer: Claws Mail 3.7.0 (GTK+ 2.14.7; x86_64-redhat-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org > What is the benefit of this? I believe the "benefit" is that a certain posters proprietary virtualisation product works better. > I can see at least one immediate downside: some timeout values in the > kernel are still maintained in units of HZ (like poll, I believe), and > so with a lower HZ value we'll have higher roundoff errors. And HZ=100 actually causes real problems for some video work (not in Europe where its just peachy). We switched to 1000Hz a very long time ago because it improved desktop feel and responsiveness. We switched to tickless to keep that behaviour with good power and idle behaviour. If we still have problems that give virtualisers hiccups then they will be giving real processor power management the same grief so I don't think meddling with HZ to harm the desktop is the right move - but if there are improvements to tickless (eg timer granularity and bunching under virtualisation) that would be far better to explore. Alan