Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1161415AbWJKV1Q (ORCPT ); Wed, 11 Oct 2006 17:27:16 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1422635AbWJKV1L (ORCPT ); Wed, 11 Oct 2006 17:27:11 -0400 Received: from smtp.osdl.org ([65.172.181.4]:41933 "EHLO smtp.osdl.org") by vger.kernel.org with ESMTP id S1161504AbWJKV1C (ORCPT ); Wed, 11 Oct 2006 17:27:02 -0400 Date: Wed, 11 Oct 2006 14:26:46 -0700 From: Andrew Morton To: john stultz Cc: Andi Kleen , lkml Subject: Re: [PATCH] i386 Time: Avoid PIT SMP lockups Message-Id: <20061011142646.eb41fac3.akpm@osdl.org> In-Reply-To: <1160596462.5973.12.camel@localhost.localdomain> References: <1160596462.5973.12.camel@localhost.localdomain> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1525 Lines: 49 On Wed, 11 Oct 2006 12:54:21 -0700 john stultz wrote: > Andrew: I think this is 2.6.19 material, but probably should go through an -mm or two. > > thanks > -john > > > This patch avoids possible PIT livelock issues seen on SMP systems (and > reported by Andi), by not allowing it as a clocksource on SMP boxes. > > However, since the PIT may no longer be present, we have to properly > handle the cases where SMP systems have TSC skew and fall back from the > TSC. Since the PIT isn't there, it would "fall back" to the TSC again. > So this changes the jiffies rating to 1, and the TSC-bad rating value to > 0. > > Thus you will get the following behavior priority on i386 systems: > > tsc [if present & stable] > hpet [if present] > cyclone [if present] > acpi_pm [if present] > pit [if UP] > jiffies > > Rather then the current more complicated: > tsc [if present & stable] > hpet [if present] > cyclone [if present] > acpi_pm [if present] > pit [if cpus < 4] Actually <=4, and that matters: there are a lot of 4-ways. > tsc [if present & unstable] > jiffies > So this patch has the potential to screw up people who have 2-way or 4-way, no hpet/pm-timer and dodgy TSCs. Wouldn't it be better to fix the livelock? What's causing it? - 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/