From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S262440AbULOSWx (ORCPT ); Wed, 15 Dec 2004 13:22:53 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S262437AbULOSVN (ORCPT ); Wed, 15 Dec 2004 13:21:13 -0500 Received: from mail-relay-4.tiscali.it ([213.205.33.44]:24773 "EHLO mail-relay-4.tiscali.it") by vger.kernel.org with ESMTP id S262436AbULOSUq (ORCPT ); Wed, 15 Dec 2004 13:20:46 -0500 Date: Wed, 15 Dec 2004 19:20:12 +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: <20041215182012.GH16322@dualathlon.random> References: <20041213002751.GP16322@dualathlon.random> <200412142159.23488.gene.heskett@verizon.net> <20041215091741.GA16322@dualathlon.random> <200412151144.38785.gene.heskett@verizon.net> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <200412151144.38785.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 Wed, Dec 15, 2004 at 11:44:38AM -0500, Gene Heskett wrote: > The HZ=1000 is the culprit? HZ=1000 isn't the culprit. The culprit is the >1msec latency of the usb irq, but that wouldn't be visible with HZ 100 (for this specific case HZ=100 would only be a band-aid). > Onboard AC-97 audio of course. Crappy stuff... [..] I doubt it's the chip, but only the motherboard to blame. My laptop has the ac97 but no HZ sound out of it. > translate to 10 millisecond intervals. If you had a 4 millisecond > latency, > that would be spread over 4 of the 1000 hz interrupts. That sounds > rather confusing to the service routine I imagine. The ones that get confused are the system time and the jiffies, the rest of the system can deal with long irq delays. The tick adjustment was exactly implemented so that the jiffies and system time wouldn't get confused anymore, but it just confuses it the other way around in my current experience. > I'll do that just for grins & report back. Ok.