Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S965077AbVITS7u (ORCPT ); Tue, 20 Sep 2005 14:59:50 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S965079AbVITS7u (ORCPT ); Tue, 20 Sep 2005 14:59:50 -0400 Received: from e32.co.us.ibm.com ([32.97.110.150]:11203 "EHLO e32.co.us.ibm.com") by vger.kernel.org with ESMTP id S965077AbVITS7t (ORCPT ); Tue, 20 Sep 2005 14:59:49 -0400 Subject: Re: [discuss] Re: [PATCH] x86-64: Fix bad assumption that dualcore cpus have synced TSCs From: john stultz To: Andi Kleen Cc: Andrew Morton , lkml , discuss@x86-64.org In-Reply-To: <20050919194934.GC12810@verdi.suse.de> References: <1127157404.3455.209.camel@cog.beaverton.ibm.com> <20050919193105.GA12810@verdi.suse.de> <1127158937.3455.214.camel@cog.beaverton.ibm.com> <20050919194934.GC12810@verdi.suse.de> Content-Type: text/plain Date: Tue, 20 Sep 2005 11:59:45 -0700 Message-Id: <1127242785.11080.20.camel@cog.beaverton.ibm.com> Mime-Version: 1.0 X-Mailer: Evolution 2.2.3 (2.2.3-2.fc4) Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1675 Lines: 42 On Mon, 2005-09-19 at 21:49 +0200, Andi Kleen wrote: > On Mon, Sep 19, 2005 at 12:42:16PM -0700, john stultz wrote: > > On Mon, 2005-09-19 at 21:31 +0200, Andi Kleen wrote: > > > On Mon, Sep 19, 2005 at 12:16:43PM -0700, john stultz wrote: > > > > This patch should resolve the issue seen in bugme bug #5105, where it > > > > is assumed that dualcore x86_64 systems have synced TSCs. This is not > > > > the case, and alternate timesources should be used instead. > > > > > > > > > I asked AMD some time ago and they told me it was synchronized. > > > The TSC on K8 is C state invariant, but not P state invariant, > > > but P states always happen synchronized on dual cores. > > > > > > So I'm not quite convinced of your explanation yet. > > > > Would a litter userspace test checking the TSC synchronization maybe > > shed additional light on the issue? > > Sure you can try it. So, bugzilla.kernel.org has (temporarily at least) lost the reports from yesterday, but from the email i got, folks using my TSC consistency check that I posted were seeing what appears to be unsynched TSCs on dualcore AMD systems. Personally I suspect that the powernow driver is putting the cores independently into low power sleep and the TSCs are being independently halted, causing them to become unsynchronized. Do you still feel there is some other issue here? Any ideas for shaking out whatever else might in play? thanks -john - 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/