Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1760191AbYB2O1k (ORCPT ); Fri, 29 Feb 2008 09:27:40 -0500 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1758690AbYB2O1a (ORCPT ); Fri, 29 Feb 2008 09:27:30 -0500 Received: from bombadil.infradead.org ([18.85.46.34]:53223 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1758518AbYB2O13 (ORCPT ); Fri, 29 Feb 2008 09:27:29 -0500 Subject: Re: Can Linux kernel handle unsynced TSC? From: Peter Zijlstra To: Zhao Forrest Cc: linux-kernel@vger.kernel.org, kvm-devel@lists.sourceforge.net In-Reply-To: References: <1204281823.6243.78.camel@lappy> Content-Type: text/plain Date: Fri, 29 Feb 2008 15:27:21 +0100 Message-Id: <1204295241.6243.108.camel@lappy> Mime-Version: 1.0 X-Mailer: Evolution 2.21.90 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1112 Lines: 28 On Fri, 2008-02-29 at 22:20 +0800, Zhao Forrest wrote: > On 2/29/08, Peter Zijlstra wrote: > > > > On Fri, 2008-02-29 at 16:55 +0800, Zhao Forrest wrote: > > > Sorry for reposting it. > > > > > > For example, > > > 1 rdtsc() is invoked on CPU0 > > > 2 process is migrated to CPU1, and rdtsc() is invoked on CPU1 > > > 3 if TSC on CPU1 is slower than TSC on CPU0, can kernel guarantee > > > that the second rdtsc() doesn't return a value smaller than the one > > > returned by the first rdtsc()? > > > > No, rdtsc() goes directly to the hardware. You need a (preferably cheap) > > clock abstraction layer on top if you need this. > > Thank you for the clarification. I think gettimeofday() is such kind > of clock abstraction layer, am I right? Yes, gtod is one such a layer, however it fails the 'cheap' test for many definitions of cheap. -- 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/