From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S266582AbUHQTBf (ORCPT ); Tue, 17 Aug 2004 15:01:35 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S266604AbUHQTBf (ORCPT ); Tue, 17 Aug 2004 15:01:35 -0400 Received: from e1.ny.us.ibm.com ([32.97.182.101]:59091 "EHLO e1.ny.us.ibm.com") by vger.kernel.org with ESMTP id S266582AbUHQTBa (ORCPT ); Tue, 17 Aug 2004 15:01:30 -0400 Subject: Re: boot time, process start time, and NOW time From: john stultz To: Albert Cahalan Cc: Andrew Morton OSDL , OGAWA Hirofumi , linux-kernel mailing list , voland@dmz.com.pl, nicolas.george@ens.fr, kaukasoi@elektroni.ee.tut.fi, tim@physik3.uni-rostock.de, george anzinger , david+powerix@blue-labs.org In-Reply-To: <1092698648.2301.1250.camel@cube> References: <1087948634.9831.1154.camel@cube> <87smcf5zx7.fsf@devron.myhome.or.jp> <20040816124136.27646d14.akpm@osdl.org> <1092698648.2301.1250.camel@cube> Content-Type: text/plain Message-Id: <1092769231.2429.115.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Ximian Evolution 1.4.5 (1.4.5-7) Date: Tue, 17 Aug 2004 12:00:31 -0700 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Mon, 2004-08-16 at 16:24, Albert Cahalan wrote: > On Mon, 2004-08-16 at 15:41, Andrew Morton wrote: > > > Where did this all end up? Complaints about > > wandering start times are persistent, and it'd > > be nice to get some fix in place... > > If you're interested in reducing (not solving) > the problem for the 2.6.x series, you might change > HZ to something that works better with the PIT. > > Here is a table showing % error for various HZ choices: > > wrongness_% HZ_diff PIT_# HZ actual_HZ > -0.00150855 -0.001509 11932 100 99.998491 > -0.00150855 -0.009474 1900 628 627.990526 > -0.00083809 -0.003051 3278 364 363.996949 > -0.00083809 -0.008389 1192 1001 1000.991611 > +0.00000000 +0.000000 14551 82 82.000000 > +0.00008381 +0.000304 3287 363 363.000304 > +0.00008381 +0.000435 2299 519 519.000435 > +0.00008381 +0.000525 1903 627 627.000525 > +0.01525566 +0.152557 1193 1000 1000.152557 > +0.01860917 +0.190558 1165 1024 1024.190558 > > As you can see, 1000 HZ and 1024 HZ are really bad. > They're worse than typical quartz crystal variation. > > The old 100 HZ tick was just barely tolerable. > While 82 is perfect, it's a bit low. :-( > > Some of the other choices are nice. How about 363, > 519, or 627? What about 1001? That looks reasonably accurate. thanks -john