From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262308AbULOJTr (ORCPT ); Wed, 15 Dec 2004 04:19:47 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262278AbULOJS2 (ORCPT ); Wed, 15 Dec 2004 04:18:28 -0500 Received: from mail-relay-1.tiscali.it ([213.205.33.41]:15071 "EHLO mail-relay-1.tiscali.it") by vger.kernel.org with ESMTP id S262308AbULOJRz (ORCPT ); Wed, 15 Dec 2004 04:17:55 -0500 Date: Wed, 15 Dec 2004 10:17:41 +0100 From: Andrea Arcangeli To: Gene Heskett Cc: linux-kernel@vger.kernel.org, Pavel Machek , Zwane Mwaikambo , Con Kolivas Subject: Re: USB making time drift [was Re: dynamic-hz] Message-ID: <20041215091741.GA16322@dualathlon.random> References: <20041213002751.GP16322@dualathlon.random> <20041214220239.GA19221@elf.ucw.cz> <20041214231649.GR16322@dualathlon.random> <200412142159.23488.gene.heskett@verizon.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200412142159.23488.gene.heskett@verizon.net> X-GPG-Key: 1024D/68B9CB43 13D9 8355 295F 4823 7C49 C012 DFA1 686E 68B9 CB43 X-PGP-Key: 1024R/CB4660B9 CC A0 71 81 F4 A0 63 AC C0 4B 81 1D 8C 15 C8 E5 User-Agent: Mutt/1.5.6i Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 14, 2004 at 09:59:23PM -0500, Gene Heskett wrote: > Which way? I was running quite fast here, several minutes an In the future, if I disable the logic it goes in the past at the same speed it was previously going in the future. > hour, then I discovered the tickadj command, found its default > was 10000, and started reducing it. At 9926, I'm staying within > a sec an hour now. I have no idea when this started, I didn't That seems quite an hack, note I did an hack too and it make the drift much smaller (it gets manageable). But our modifications are wrong. The point is that this didn't happen with HZ=100, so it's not that tickadj is wrong, it's the tick adjustment code that doesn't work. You may want to recompile your kernel with HZ=100 and verify it goes away (I didn't verify myself, but I verified the max irq latency I get is 4msec, and in turn I'm sure HZ=100 would fix it)