Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S263994AbUCPRaJ (ORCPT ); Tue, 16 Mar 2004 12:30:09 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S264163AbUCPRaB (ORCPT ); Tue, 16 Mar 2004 12:30:01 -0500 Received: from ns2.uk.superh.com ([193.128.105.170]:30128 "EHLO smtp.uk.superh.com") by vger.kernel.org with ESMTP id S263994AbUCPR05 (ORCPT ); Tue, 16 Mar 2004 12:26:57 -0500 Date: Tue, 16 Mar 2004 17:22:24 +0000 From: Richard Curnow To: Albert Cahalan Cc: linux-kernel mailing list , arjanv@redhat.com, peterw@aurema.com, ak@muc.de Subject: Re: finding out the value of HZ from userspace Message-ID: <20040316172224.GF17627@malvern.uk.w2k.superh.com> Mail-Followup-To: Albert Cahalan , linux-kernel mailing list , arjanv@redhat.com, peterw@aurema.com, ak@muc.de References: <1079453698.2255.661.camel@cube> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1079453698.2255.661.camel@cube> User-Agent: Mutt/1.5.6i X-OriginalArrivalTime: 16 Mar 2004 17:27:30.0733 (UTC) FILETIME=[F5E205D0:01C40B7B] Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1364 Lines: 32 * Albert Cahalan [2004-03-16]: > > Fortunately this is a fresh new reason to beg Linus for > some data. (all previous arguments have been rejected) > What would be useful for you? > > HZ (-1 for tickless?) > USER_HZ > freq_scale > some boolean to indicate ppc-like (pure cycle counter) time > ??? freq_scale would be a good starting point, I think. However, there is worse. There is bounds checking on the txc.freq argument to adjtimex(). IIRC the bounds have changed at various points in the kernel history, but at one time the limit was +/- 100ppm. At the time, I had a mobo with a -300ppm clock error. To cope with this, chrony modifies txc.tick to take out the gross error as well as txc.freq to adjust the fine error. Therefore, it needs some idea of how tick and freq inter-relate, and what the valid range of values for tick is. This is another mess. I need to go away and think some more to know info from the kernel side would make the problem easier to code for, though. -- Richard \\\ SH-4/SH-5 Core & Debug Architect Curnow \\\ SuperH (UK) Ltd, Bristol - 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/